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Vector.pdf

This document provides an overview of a GIS lecture on vector geographic information systems. It discusses key concepts in GIS including components of a GIS, geographic coordinate systems, map projections, vector data models like the spaghetti and topological models, and data capture methods. Recommendations are also made for standard projections and reference systems used by the Food and Agriculture Organization.

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GIS Lecture 1. Introduction to Vector Geographic Information Systems Data Conversion/Entry (GIS, Databases) November 6 – 10, 2006 Freetown, Sierra Leone
Lecture Outline • Components of a GIS • Basic GIS Concepts • Geographic Coordinate Systems • Projections • Vector Data Models • Spaghetti Data Model • Topological Data Model • Triangulated Irregular Networks (TINs) • Data Capture Systems •Digitizing •Scanning •GPS • Vector Editing • Vector GIS Functions and Analysis
So, What is a GIS • A system for capturing, storing, checking, manipulating, analysingand displaying data which are spatially referenced to the Earth (DoE, 1987) • Any manual or computer based set of procedures used to store and manipulate geographically referenced data (Aronoff, 1989) • A database system in which most of the data are spatially indexed, and upon which a set of procedures operated in order to answer queries about spatial entities in the database. (Smith, 1987) • A system with advanced geo-modeling capabilities. (Koshkariov, et. al. 1986) Arthur J. Lembo, Jr. Cornell University
Components of GIS Something has to make all of these applications go together. That something includes the basic components of GIS. As we said, GIS is an integrated system of geography and information tied together. The main components of a GIS include: •People •Hardware •Software Many people see GIS as an integrative technology, because it helps tie many different geospatial activities together. In fact, the different geospatial activities are the very thing that helped create GIS in the first place! For example, GIS links many parallel developments such as: •Computer automated drafting •Cartography / Surveying •Photogrammetry •Digital Image Processing •Global Positioning System •Statistics… among other technologies Each of these disciplines, among others, have greatly contributed to the development of GIS technology.
Why is GIS Important • A Ubiquitous Tool • Environmental Analysis • Engineering Design • Business Geographics • Social Services • Better Government
Basic Concepts of GIS As we said, the definition of GIS, at least the way we present it here is rather long. But, the concepts of GIS are quite simple, especially if you break it down into its component words: • G stands for geographic, so we know that GIS has something to do with geography. • I stands for information, so we know that GIS has something to do with information, namely geographic information. • S stands for system, so we know that GIS is an integrated system of geography and information tied together. • Most people agree that over 80% of the information related to government operations have a geographic component. Therefore, a system that integrates this information together is quite valuable. We shall see how a geographic information system tied geography and information together…. Arthur J. Lembo, Jr. Cornell University
0º 0º 0º 0º Prime Meridian Prime Meridian Equator Equator (Longitude) (Longitude) (Latitude) (Latitude) 10º N 10º N 30º N 30º N 10º S 10º S Geographic Coordinate Systems (GCS) Latitude and Longitude
Spheroid Semimajor Axis (m) Semiminor Axis (m) Clarke 1866 6,378,206.4 6,356,583.8 GRS1980 6,378,137.0 6,356,752.31414 WGS1984 6,378,137.0 6,356,752.31424 Spheroids and Ellipsoids
Ellipsoid Parameters Ellipsoid Parameters In ILWIS In ArcGIS
Units: Geographic Coordinates Units: • Degrees Minutes Seconds • Decimal Degrees 60 minutes = 1 degree 60 seconds = 1 minute 64o 30’ 15” = decimal degrees? Answer: = 64 + (30/60) + (15/(60*60)) = 64.541666 DD
A Datum is Defined by • A Spheroid • Datum origin point • Orientation of Geographic Coordinate (i.e. Equator and Prime Meridian)
A projected coordinate system is defined on a flat, two-dimensional surface. Unlike a geographic coordinate system, a projected coordinate system has constant lengths, angles, and areas across the two dimensions. A projected coordinate system is always based on a geographic coordinate system that is based on a sphere or spheroid. Projected Coordinate Systems Moving from 3-D to 2-D!
Understanding mapping: error There are six main types of distortion in mapping: •shape •distance •area •direction •scale •angle
Understanding mapping: projection Azimuthal projection Cylindrical projection Conic projection Different projections have their own characteristics and uses. They all distort the properties of the Earth, but do so differently.
Cylindrical surface Earth intersects the cylinder on two small circles. All points along both circles have no scale distortion.
Mercator Projection A Cylindrical Projection
Africa - Lambert Azimuthal Equal-Area 5N, 20E A Conic Projection This is the African Continental Projection Recommended by the FAO
A good reference: http://gis.esri.com/library/userconf/proc98/PROCEED/TO850/PAP844/P844.HTM#appendix%203 The Interrupted Goode Homolosine Projection (Goode's) Combining twelve instances of the Mollweide and Sinusoidal Map Projections Many Global Datasets/Imagery are made available in this projection, including MODIS Imagery
UTM Projection • Universe Transverse Mercator • Conformal projection (shapes are preserved) • Cylindrical surface • Two standard meridians • Zones are 6 degrees of longitude wide
UTM Zones
Sierra Leone Landsat MSS Imagery In UTM (Universal Transverse Mercator) Projection In ArcGIS In ILWIS Notice the same parameters in both UTM Zone 28
Reference: Food and Agriculture Organization of the United Nations. SPATL-PAIA/GIS Doc. 01 2003-04-28 FAO Interdisciplinary Database: Spatial Standards and Norms Draft Technical Report Map Projections • There are no absolute standards that can generally be applied for map projections, since there is no absolute better projection than another. • The choice of the projection depends on the considered portion of the world and on the purpose for which the map is to be used for. • However, for the objective of standardization and data exchange, the intent is to find a suitable set of map projections which can provide a good representation of the areas under examination (minimizing distortions of shapes and areas) and that can be handled by most of the commercial GIS packages in use in FAO.
FAO Recommended Standard Projections • All dataset types: un-projected (Geographic) • Global datasets: Mollweide • Continental datasets: Lambert Azimuthal Equal Area • National datasets: Lambert Conformal Conic or Albers Equal Area Conic • Sub-national or tiled datasets: Universal Transverse Mercator (UTM) Food and Agriculture Organization of the United Nations. SPATL-PAIA/GIS Doc. 01 2003-04-28 FAO Interdisciplinary Database: Spatial Standards and Norms Draft Technical Report
FAO Recommended Datum and Spheroid Standards Reference system based on WGS 84 datum and IAG-GRS80 spheroid Most of the global and continental datasets are referenced according to the WGS 84 datum based on IAG-GRS80 spheroid. Being a global datum which fairly represents every location on the earth’s surface, it is convenient for small-scale data and it is recommended for FAO use. In addition, datasets currently produced by the UN Cartographic Section use the same reference system. Food and Agriculture Organization of the United Nations. SPATL-PAIA/GIS Doc. 01 2003- 04-28 FAO Interdisciplinary Database: Spatial Standards and Norms Draft Technical Report
Continent Recommended Projection and Projection Parameters North America Lambert Azimuthal Equal Area with center in 50N, 100W South America Lambert Azimuthal Equal Area with center in 15N, 60W Europe Lambert Azimuthal Equal Area with center in 55N, 20E Africa Lambert Azimuthal Equal Area with center in 5N, 20E Asia Lambert Azimuthal Equal Area with center in 45N, 100E Australia Lambert Azimuthal Equal Area with center in 15S, 135E Antarctica Lambert Azimuthal Equal Area centered on the South Pole FAO Recommended Continental Scale Projections Food and Agriculture Organization of the United Nations. SPATL-PAIA/GIS Doc. 01 2003- 04-28 FAO Interdisciplinary Database: Spatial Standards and Norms Draft Technical Report
Africa - Lambert Azimuthal Equal-Area 5N, 20E
Antarctica - Lambert Azimuthal Equal-Area 90S, 0E
Vector GIS Data Models • Relational Databases •Vector Data Models • Spaghetti Data Model • Topological Data Model
(Taken from Arnoff 1991) The Relational Data Model • Information stored in simple two dimensional tables • Organization is simple to understand and communicate • Tables and be linked by a common field/fields • Redundant data storage minimized • More Flexible than other models. • Queries can be somewhat slower than other models.
Storage of GIS Attribute Information in a Relational Data Base
The Spaghetti Data Model • A point is encoded as a single XY coordinate pair. A line is encoded as string of XY coordinate pairs. An area is represented a polygon and is recorded as a closed loop of XY coordinates that define its boundary. •Essentially a collection of coordinate strings with no inherent structure - hence the term spaghetti model. • Model is very simple and easy to understand. The spatial relationship between features is not encoded. •This model is very inefficient for most types of spatial analyses, since any spatial relationship must be derived from computation. (Taken from Arnoff 1991)
• Advantages: - the Spaghetti data model is very simple and easy to understand. • Disadvantages: - lines between adjacent areas must be digitized twice. - the spatial relationships between features are not retained. - this model is very inefficient for most types of spatial analyses (since any spatial relationship must be derived from computation). The Spaghetti Data Model
The Topological Data Model (Taken from Arnoff 1991) Webster’s Dictionary Definition of Topology: A branch of mathematics concerned with those properties of geometric configuration. • Note: Polygons can have islands within them. Polygon C is an island within polygon B. This is indicated in ARCS listed for polygon B by a zero proceeding the list of arcs.
• Most widely used method of encoding spatial relationships in a GIS (eg. ArcInfo). • From the topology alone (ie the three topology tables), analysis of the relative position of the map elements can be done. • Since all spatial relationships are explicitly defined in the topology tables (eg. Connectivity and Contiguity) spatial queries using the topology tables can be processed very quickly. Example. Find all features within Polygon B. • To do spatial queries in non-topological GISs (such as ArcView) is much more computer intensive and requires the use of the coordinate data. Topological Data Model
• Advantages: - spatial relations are retained - from the topology alone analysis of the relative position of the map elements can be done - spatial queries using the topology tables can be processed very quickly • Disadvantages: - more complex data structure - map updating requires updating topology The Topological Data Model
Comparison of the Topological vs. Non-topological A – As you would expect in ArcView 3.* (non topological B – As you would expect in ArcInfo Workstation (topological) A) B) Compare these tables to the note: Fnode# = Start Node Tnode# = End Node Lpoly# = Left Polygon Rpoly# = Right Polygon
Triangled Irregular Networks (TINs) • A TIN is a vector-based topological data model. A TIN represents the surface as a set of interconnected triangular facets. For each of the three vertices, the XY coordinate (geographic location) and the Z coordinate (elevation or other) values are encoded. • The coordinate data and topology for the TIN are stored in a set of tables • TINs are irregularly spaced such that they are dense in areas of rapidly changing terrain and sparse in areas of relatively flat terrain. • In the TIN, each triangle forms a plane from which the terrain parameters of slope and slope aspect can be calculated and stored as attributes. • The generated surface passes through all the data points (exact Interpolator)
A Comparison of Raster, Vector and TIN Data Structures For Representing Elevation
Topological Data Structure of a Triangled Irregular Network
Topographic Map and the Corresponding TIN Representation Topographic Map TIN Representation
X - axis Y - axis 42 35 32 28 26 X Y Z 1 1 26 2 3 28 4 3 32 3 5 42 5 4 35 3 4 ? Triangled Irregular Networks (TINs) The elevation at any point on the surface can be calculated. All that is required is the x,y and z coordinates of triangle it is within. Z = a + bx + cy - where a,b and c are constants. For the example to the left 42 = a + 3b +5c 32 = a + 4b +2c 28 = a +2b +3c From which: z = 4.8 + 4.4x + 4.8y and substituting coordinates (3,4) z = 37.2
Advantages of TINs STORAGE: TINs are an efficient storage model. Because the size of each facet is variable, smaller triangles and therefore a more detailed representation can be provided where there is a high density of data points. FEATURE DEFINITION: Break-point features in the terrain, such as ridge lines, faults, valley bottoms, streams can be accurately encoded by using a higher density of elevation points. As a result, these features can be precisely encoded in a TIN. In a grid representation these same features may be smoothed. Although there are many advantages to representing data in a TIN, they are commonly translated to the raster model. This is largely due, that once in this format it is currently easier to model and the data can be easily integrated with other image data, such as remote sensing imagery.
What is Digitizing? • The most common method of converting existing maps into digital format. • Secure source map to digitizing tablet. • Select and record control points. • Trace over the map with cursor. • Crosshairs on cursor must line up exactly with the features you are digitizing. • The digitizer records coordinates as x and y tablet coordinates and then transforms them to the map coordinate system. • Edit and correct the data. Cursor Digitizing tablet
Data Capture by Scanning Because the computer allows us to zoom far into images we can work with the mouse and scanned image to allow much greater accuracy than is possible with a digitizing tablet. Scanners are much less expensive than digitizers, are much more accurate. Most people are familiar with scanners, as they can be purchased rather cheaply in office supply stores. However, the scanners you are most familiar with probably only copy legal size paper. For mapping purposes, scanners have to be much larger, with the ability to accommodate sheet sizes greater than 34”, as shown here. These devices allow a user to scan a map in the computer and perform digitizing on the computer screen (this is called “heads-up” digitizing), thus eliminating the need for a digitizing tablet.
Field Data Collection Directly with Hand Held GPS enabled Devices Captured coordinates and attributes can be entered directly into a GIS
Geometric Correction Note this is the same process you use to: • Register your digitizing table to your selected Coordinate System. • Register your raw Satellite or Airborne Raster Imagery to your selected Coordinate System • Register your Scanned Map to your selected Coordinate System.
Geometric Correction Moving from Local Coordinates to Easting and Northing Raw Image Corrected Image c r n n’ e e’ c’ r’ e’=f(c,r) n’=f(c,r)
X1=ao + a1x + a2y + a3xy + a4x2 + a5y2 + a6x2y + a7xy2 + a8x3 + a9y3 1st order 2nd order 3rd order Y1=bo + b1x + b2y + b3xy + b4x2 + b5y2 + b6x2y + b7xy2 + b8x3 + b9y3 1st order 2nd order 3rd order POLYNOMIAL EQUATIONS FOR X1, Y1 Notes: • Where X1,Y1 are the coordinates in the uncorrected image generated from the corrected matrix system x,y coordinates. • a and b are constants. Source: PCI Manual
The Vector Editing Environment in ArcGIS
The Vector Editing Environment in ILWIS
Vector GIS Functions and Analysis
Vector GIS Functions and Analysis in ILWIS
A couple of the Vector Tools in ArcGIS – Buffer Wizard and the GeoProcessing Wizard
NETWORK FUNCTIONS • A Network is a set of interconnected linear features that form a pattern or framework (e.g.. Streams, Roads etc.). • Network Analysis requires a networked and topologically structured vector data layer. • Networks are commonly used for moving resources from one location to another.
Example of a Stream Network Query Extract all Second-Order Streams (Red) And then Extract Associated Second-Order Catchments Red Vectors Indicating Strahler Second-Order Streams
Network Analysis Network Analysis usually involve four components: • A set of resources (such as goods to be delivered); • One or more locations where the resources are located (such as the warehouse where the goods are stored); • An objective. To deliver the resources to a set of destinations - or to provide a minimum level of service (such as a police station); • A set of constraints that places limits on how the objectives can be met (such as a maximum speed, one-way street etc.).
A GIS is used to perform three principal types of Network analysis: • Prediction of Network loading • Route Optimization • Resource Allocation
Route Optimization Examples: 1) Emergency routing of ambulances, fire, police vehicles 2) Airline Scheduling 3) Routing of Bus Services, Mail Serives etc.
Resource Allocation Examples: 1) Division of a metropolitan area into zones that can be effectively serviced by individual police and fire stations. 2) Where geographically to add additional ambulance stations to increase overall objectives.
NETWORK ANALYSIS • Network Analysis is not well suited to raster GIS. • In ArcInfo is called NETWORK Module. • In ArcView is called Network Analyst.
Connectivity Functions • Connectivity operations are used to characterize spatial units that are connected according to a set of pre-defined rules. • Every connectivity function requires: - definition of the way spatial elements are interconnected - the rules that control the movements along these interconnections - a unit of measurement.
Connectivity functions • Some of the most commonly used connectivity functions in raster are included in the following three groups: - Contiguity functions - Proximity functions - Spread functions
Connectivity functions Contiguity functions • Contiguity functions are usually applied to identify contiguous areas with specific size and characteristics. • A contiguous area consists of a group of spatial features that share one or more specified characteristics and form a unit. • Definition of contiguous areas changes with applications. • Example of application: search for land units to be used as parks. - Include: forests, rivers and swamps - under these conditions: contiguous land unit must have a minimum area of 400 Km2 with no sections narrower than 10 Km for the forests and 5 km for the swamps.
Forest Swamp River Fields Example of Contiguity Analysis Land Cover Map Contiguous Areas Conditions for contiguity: Land cover types: forest, swamps and rivers Minimum area: 400 Km2 Minimum section: 10 Km for forest 5 Km for swamp
Connectivity Functions Proximity Functions • Proximity functions measure the distance between features. • The most common measurement units are length and travel time. • Proximity functions require the definition of four parameters: 1. the target (e.g. a hospital, a road, a house) 2. a unit of measure (e.g. distance in meters, travel time in minutes) 3. a function to calculate proximity (e.g. Euclidean distance) 4. the area of interest. • A proximity analysis usually results in the generation of a buffer zone around one or more map elements.
Proximity Functions • Examples of proximity analyses are: - make a distance map from a given river within a watershed area by generating a buffer zone of increasing distances around the river (e.g. 0-250 m, 250-500 m, 500-1000 m, >1000 m). - define protected areas where building is not permitted around a wetland by generating a buffer zone of a specified width around the wetland. - analyze the pattern of noise propagation from an airport by calculating the distance of each location from the sound source and the expected rate of decrease in noise level with increasing distance.
Example of buffer zone generation River 0 - 250 m 250 - 500 m
Connectivity Functions Spread Functions • Spread functions evaluate phenomena that spread or accumulate with distance. • The output map is also called accumulation or friction surface. • A spread operation can be thought of as moving step-by-step outward in all directions from one or more starting points and calculating a variable at each successive step.
Example of application using a spread function • Spread function results can be presented as contour maps. In this figure: contours represent distances in Km away from starting point A. The shortest distance between A and B is indicated by the straight line connecting them. In this simple case spread and proximity functions are the same. A B + 1 2 3 4 5 6 7
A B + 1 2 3 4 5 6 7 Absolute Barrier Example of application using a spread function In the case of an absolute barrier, such as a lake that obstacles truck travel, the shortest travel distance has to take into account the obstacle (red line). This type of analysis involving obstacles can not be accommodated by proximity functions.
Examples of Applications using spread functions • Transportation time and cost from and to selected features (e.g. railways, roads, mines). • Monitoring the spreading of pollution. • Mapping flooded areas. • Terrain trafficability: it is a complex analysis often used in military operations. The trafficability (or easy and speed of movement) depends on many variables such as: topography, land cover type, transportation and season.

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Vector.pdf

  • 1.
    GIS Lecture 1. Introductionto Vector Geographic Information Systems Data Conversion/Entry (GIS, Databases) November 6 – 10, 2006 Freetown, Sierra Leone
  • 2.
    Lecture Outline • Componentsof a GIS • Basic GIS Concepts • Geographic Coordinate Systems • Projections • Vector Data Models • Spaghetti Data Model • Topological Data Model • Triangulated Irregular Networks (TINs) • Data Capture Systems •Digitizing •Scanning •GPS • Vector Editing • Vector GIS Functions and Analysis
  • 3.
    So, What isa GIS • A system for capturing, storing, checking, manipulating, analysingand displaying data which are spatially referenced to the Earth (DoE, 1987) • Any manual or computer based set of procedures used to store and manipulate geographically referenced data (Aronoff, 1989) • A database system in which most of the data are spatially indexed, and upon which a set of procedures operated in order to answer queries about spatial entities in the database. (Smith, 1987) • A system with advanced geo-modeling capabilities. (Koshkariov, et. al. 1986) Arthur J. Lembo, Jr. Cornell University
  • 4.
    Components of GIS Somethinghas to make all of these applications go together. That something includes the basic components of GIS. As we said, GIS is an integrated system of geography and information tied together. The main components of a GIS include: •People •Hardware •Software Many people see GIS as an integrative technology, because it helps tie many different geospatial activities together. In fact, the different geospatial activities are the very thing that helped create GIS in the first place! For example, GIS links many parallel developments such as: •Computer automated drafting •Cartography / Surveying •Photogrammetry •Digital Image Processing •Global Positioning System •Statistics… among other technologies Each of these disciplines, among others, have greatly contributed to the development of GIS technology.
  • 5.
    Why is GISImportant • A Ubiquitous Tool • Environmental Analysis • Engineering Design • Business Geographics • Social Services • Better Government
  • 7.
    Basic Concepts ofGIS As we said, the definition of GIS, at least the way we present it here is rather long. But, the concepts of GIS are quite simple, especially if you break it down into its component words: • G stands for geographic, so we know that GIS has something to do with geography. • I stands for information, so we know that GIS has something to do with information, namely geographic information. • S stands for system, so we know that GIS is an integrated system of geography and information tied together. • Most people agree that over 80% of the information related to government operations have a geographic component. Therefore, a system that integrates this information together is quite valuable. We shall see how a geographic information system tied geography and information together…. Arthur J. Lembo, Jr. Cornell University
  • 8.
    0º 0º 0º 0º Prime Meridian Prime Meridian Equator Equator (Longitude) (Longitude) (Latitude) (Latitude) 10ºN 10º N 30º N 30º N 10º S 10º S Geographic Coordinate Systems (GCS) Latitude and Longitude
  • 9.
    Spheroid Semimajor Axis (m) Semiminor Axis(m) Clarke 1866 6,378,206.4 6,356,583.8 GRS1980 6,378,137.0 6,356,752.31414 WGS1984 6,378,137.0 6,356,752.31424 Spheroids and Ellipsoids
  • 10.
  • 11.
    Units: Geographic Coordinates Units: •Degrees Minutes Seconds • Decimal Degrees 60 minutes = 1 degree 60 seconds = 1 minute 64o 30’ 15” = decimal degrees? Answer: = 64 + (30/60) + (15/(60*60)) = 64.541666 DD
  • 12.
    A Datum isDefined by • A Spheroid • Datum origin point • Orientation of Geographic Coordinate (i.e. Equator and Prime Meridian)
  • 13.
    A projected coordinatesystem is defined on a flat, two-dimensional surface. Unlike a geographic coordinate system, a projected coordinate system has constant lengths, angles, and areas across the two dimensions. A projected coordinate system is always based on a geographic coordinate system that is based on a sphere or spheroid. Projected Coordinate Systems Moving from 3-D to 2-D!
  • 14.
    Understanding mapping: error There aresix main types of distortion in mapping: •shape •distance •area •direction •scale •angle
  • 16.
    Understanding mapping: projection Azimuthal projection Cylindricalprojection Conic projection Different projections have their own characteristics and uses. They all distort the properties of the Earth, but do so differently.
  • 17.
    Cylindrical surface Earth intersectsthe cylinder on two small circles. All points along both circles have no scale distortion.
  • 18.
  • 19.
    Africa - LambertAzimuthal Equal-Area 5N, 20E A Conic Projection This is the African Continental Projection Recommended by the FAO
  • 20.
    A good reference:http://gis.esri.com/library/userconf/proc98/PROCEED/TO850/PAP844/P844.HTM#appendix%203 The Interrupted Goode Homolosine Projection (Goode's) Combining twelve instances of the Mollweide and Sinusoidal Map Projections Many Global Datasets/Imagery are made available in this projection, including MODIS Imagery
  • 21.
    UTM Projection • UniverseTransverse Mercator • Conformal projection (shapes are preserved) • Cylindrical surface • Two standard meridians • Zones are 6 degrees of longitude wide
  • 22.
  • 23.
    Sierra Leone LandsatMSS Imagery In UTM (Universal Transverse Mercator) Projection In ArcGIS In ILWIS Notice the same parameters in both UTM Zone 28
  • 24.
    Reference: Food andAgriculture Organization of the United Nations. SPATL-PAIA/GIS Doc. 01 2003-04-28 FAO Interdisciplinary Database: Spatial Standards and Norms Draft Technical Report Map Projections • There are no absolute standards that can generally be applied for map projections, since there is no absolute better projection than another. • The choice of the projection depends on the considered portion of the world and on the purpose for which the map is to be used for. • However, for the objective of standardization and data exchange, the intent is to find a suitable set of map projections which can provide a good representation of the areas under examination (minimizing distortions of shapes and areas) and that can be handled by most of the commercial GIS packages in use in FAO.
  • 25.
    FAO Recommended Standard Projections •All dataset types: un-projected (Geographic) • Global datasets: Mollweide • Continental datasets: Lambert Azimuthal Equal Area • National datasets: Lambert Conformal Conic or Albers Equal Area Conic • Sub-national or tiled datasets: Universal Transverse Mercator (UTM) Food and Agriculture Organization of the United Nations. SPATL-PAIA/GIS Doc. 01 2003-04-28 FAO Interdisciplinary Database: Spatial Standards and Norms Draft Technical Report
  • 26.
    FAO Recommended Datumand Spheroid Standards Reference system based on WGS 84 datum and IAG-GRS80 spheroid Most of the global and continental datasets are referenced according to the WGS 84 datum based on IAG-GRS80 spheroid. Being a global datum which fairly represents every location on the earth’s surface, it is convenient for small-scale data and it is recommended for FAO use. In addition, datasets currently produced by the UN Cartographic Section use the same reference system. Food and Agriculture Organization of the United Nations. SPATL-PAIA/GIS Doc. 01 2003- 04-28 FAO Interdisciplinary Database: Spatial Standards and Norms Draft Technical Report
  • 27.
    Continent Recommended Projectionand Projection Parameters North America Lambert Azimuthal Equal Area with center in 50N, 100W South America Lambert Azimuthal Equal Area with center in 15N, 60W Europe Lambert Azimuthal Equal Area with center in 55N, 20E Africa Lambert Azimuthal Equal Area with center in 5N, 20E Asia Lambert Azimuthal Equal Area with center in 45N, 100E Australia Lambert Azimuthal Equal Area with center in 15S, 135E Antarctica Lambert Azimuthal Equal Area centered on the South Pole FAO Recommended Continental Scale Projections Food and Agriculture Organization of the United Nations. SPATL-PAIA/GIS Doc. 01 2003- 04-28 FAO Interdisciplinary Database: Spatial Standards and Norms Draft Technical Report
  • 28.
    Africa - LambertAzimuthal Equal-Area 5N, 20E
  • 29.
    Antarctica - LambertAzimuthal Equal-Area 90S, 0E
  • 30.
    Vector GIS DataModels • Relational Databases •Vector Data Models • Spaghetti Data Model • Topological Data Model
  • 31.
    (Taken from Arnoff1991) The Relational Data Model • Information stored in simple two dimensional tables • Organization is simple to understand and communicate • Tables and be linked by a common field/fields • Redundant data storage minimized • More Flexible than other models. • Queries can be somewhat slower than other models.
  • 32.
    Storage of GISAttribute Information in a Relational Data Base
  • 33.
    The Spaghetti DataModel • A point is encoded as a single XY coordinate pair. A line is encoded as string of XY coordinate pairs. An area is represented a polygon and is recorded as a closed loop of XY coordinates that define its boundary. •Essentially a collection of coordinate strings with no inherent structure - hence the term spaghetti model. • Model is very simple and easy to understand. The spatial relationship between features is not encoded. •This model is very inefficient for most types of spatial analyses, since any spatial relationship must be derived from computation. (Taken from Arnoff 1991)
  • 34.
    • Advantages: - theSpaghetti data model is very simple and easy to understand. • Disadvantages: - lines between adjacent areas must be digitized twice. - the spatial relationships between features are not retained. - this model is very inefficient for most types of spatial analyses (since any spatial relationship must be derived from computation). The Spaghetti Data Model
  • 35.
    The Topological DataModel (Taken from Arnoff 1991) Webster’s Dictionary Definition of Topology: A branch of mathematics concerned with those properties of geometric configuration. • Note: Polygons can have islands within them. Polygon C is an island within polygon B. This is indicated in ARCS listed for polygon B by a zero proceeding the list of arcs.
  • 36.
    • Most widelyused method of encoding spatial relationships in a GIS (eg. ArcInfo). • From the topology alone (ie the three topology tables), analysis of the relative position of the map elements can be done. • Since all spatial relationships are explicitly defined in the topology tables (eg. Connectivity and Contiguity) spatial queries using the topology tables can be processed very quickly. Example. Find all features within Polygon B. • To do spatial queries in non-topological GISs (such as ArcView) is much more computer intensive and requires the use of the coordinate data. Topological Data Model
  • 37.
    • Advantages: - spatialrelations are retained - from the topology alone analysis of the relative position of the map elements can be done - spatial queries using the topology tables can be processed very quickly • Disadvantages: - more complex data structure - map updating requires updating topology The Topological Data Model
  • 38.
    Comparison of theTopological vs. Non-topological A – As you would expect in ArcView 3.* (non topological B – As you would expect in ArcInfo Workstation (topological) A) B) Compare these tables to the note: Fnode# = Start Node Tnode# = End Node Lpoly# = Left Polygon Rpoly# = Right Polygon
  • 39.
    Triangled Irregular Networks(TINs) • A TIN is a vector-based topological data model. A TIN represents the surface as a set of interconnected triangular facets. For each of the three vertices, the XY coordinate (geographic location) and the Z coordinate (elevation or other) values are encoded. • The coordinate data and topology for the TIN are stored in a set of tables • TINs are irregularly spaced such that they are dense in areas of rapidly changing terrain and sparse in areas of relatively flat terrain. • In the TIN, each triangle forms a plane from which the terrain parameters of slope and slope aspect can be calculated and stored as attributes. • The generated surface passes through all the data points (exact Interpolator)
  • 40.
    A Comparison ofRaster, Vector and TIN Data Structures For Representing Elevation
  • 41.
    Topological Data Structureof a Triangled Irregular Network
  • 42.
    Topographic Map andthe Corresponding TIN Representation Topographic Map TIN Representation
  • 43.
    X - axis Y - axis 42 35 32 28 26 XY Z 1 1 26 2 3 28 4 3 32 3 5 42 5 4 35 3 4 ? Triangled Irregular Networks (TINs) The elevation at any point on the surface can be calculated. All that is required is the x,y and z coordinates of triangle it is within. Z = a + bx + cy - where a,b and c are constants. For the example to the left 42 = a + 3b +5c 32 = a + 4b +2c 28 = a +2b +3c From which: z = 4.8 + 4.4x + 4.8y and substituting coordinates (3,4) z = 37.2
  • 44.
    Advantages of TINs STORAGE:TINs are an efficient storage model. Because the size of each facet is variable, smaller triangles and therefore a more detailed representation can be provided where there is a high density of data points. FEATURE DEFINITION: Break-point features in the terrain, such as ridge lines, faults, valley bottoms, streams can be accurately encoded by using a higher density of elevation points. As a result, these features can be precisely encoded in a TIN. In a grid representation these same features may be smoothed. Although there are many advantages to representing data in a TIN, they are commonly translated to the raster model. This is largely due, that once in this format it is currently easier to model and the data can be easily integrated with other image data, such as remote sensing imagery.
  • 45.
    What is Digitizing? •The most common method of converting existing maps into digital format. • Secure source map to digitizing tablet. • Select and record control points. • Trace over the map with cursor. • Crosshairs on cursor must line up exactly with the features you are digitizing. • The digitizer records coordinates as x and y tablet coordinates and then transforms them to the map coordinate system. • Edit and correct the data. Cursor Digitizing tablet
  • 46.
    Data Capture byScanning Because the computer allows us to zoom far into images we can work with the mouse and scanned image to allow much greater accuracy than is possible with a digitizing tablet. Scanners are much less expensive than digitizers, are much more accurate. Most people are familiar with scanners, as they can be purchased rather cheaply in office supply stores. However, the scanners you are most familiar with probably only copy legal size paper. For mapping purposes, scanners have to be much larger, with the ability to accommodate sheet sizes greater than 34”, as shown here. These devices allow a user to scan a map in the computer and perform digitizing on the computer screen (this is called “heads-up” digitizing), thus eliminating the need for a digitizing tablet.
  • 47.
    Field Data CollectionDirectly with Hand Held GPS enabled Devices Captured coordinates and attributes can be entered directly into a GIS
  • 48.
    Geometric Correction Note thisis the same process you use to: • Register your digitizing table to your selected Coordinate System. • Register your raw Satellite or Airborne Raster Imagery to your selected Coordinate System • Register your Scanned Map to your selected Coordinate System.
  • 49.
    Geometric Correction Moving fromLocal Coordinates to Easting and Northing Raw Image Corrected Image c r n n’ e e’ c’ r’ e’=f(c,r) n’=f(c,r)
  • 50.
    X1=ao + a1x+ a2y + a3xy + a4x2 + a5y2 + a6x2y + a7xy2 + a8x3 + a9y3 1st order 2nd order 3rd order Y1=bo + b1x + b2y + b3xy + b4x2 + b5y2 + b6x2y + b7xy2 + b8x3 + b9y3 1st order 2nd order 3rd order POLYNOMIAL EQUATIONS FOR X1, Y1 Notes: • Where X1,Y1 are the coordinates in the uncorrected image generated from the corrected matrix system x,y coordinates. • a and b are constants. Source: PCI Manual
  • 51.
    The Vector EditingEnvironment in ArcGIS
  • 52.
    The Vector EditingEnvironment in ILWIS
  • 53.
  • 54.
    Vector GIS Functionsand Analysis in ILWIS
  • 55.
    A couple ofthe Vector Tools in ArcGIS – Buffer Wizard and the GeoProcessing Wizard
  • 56.
    NETWORK FUNCTIONS • ANetwork is a set of interconnected linear features that form a pattern or framework (e.g.. Streams, Roads etc.). • Network Analysis requires a networked and topologically structured vector data layer. • Networks are commonly used for moving resources from one location to another.
  • 57.
    Example of aStream Network Query Extract all Second-Order Streams (Red) And then Extract Associated Second-Order Catchments Red Vectors Indicating Strahler Second-Order Streams
  • 58.
    Network Analysis Network Analysisusually involve four components: • A set of resources (such as goods to be delivered); • One or more locations where the resources are located (such as the warehouse where the goods are stored); • An objective. To deliver the resources to a set of destinations - or to provide a minimum level of service (such as a police station); • A set of constraints that places limits on how the objectives can be met (such as a maximum speed, one-way street etc.).
  • 59.
    A GIS isused to perform three principal types of Network analysis: • Prediction of Network loading • Route Optimization • Resource Allocation
  • 60.
    Route Optimization Examples: 1) Emergencyrouting of ambulances, fire, police vehicles 2) Airline Scheduling 3) Routing of Bus Services, Mail Serives etc.
  • 61.
    Resource Allocation Examples: 1) Divisionof a metropolitan area into zones that can be effectively serviced by individual police and fire stations. 2) Where geographically to add additional ambulance stations to increase overall objectives.
  • 62.
    NETWORK ANALYSIS • NetworkAnalysis is not well suited to raster GIS. • In ArcInfo is called NETWORK Module. • In ArcView is called Network Analyst.
  • 63.
    Connectivity Functions • Connectivityoperations are used to characterize spatial units that are connected according to a set of pre-defined rules. • Every connectivity function requires: - definition of the way spatial elements are interconnected - the rules that control the movements along these interconnections - a unit of measurement.
  • 64.
    Connectivity functions • Someof the most commonly used connectivity functions in raster are included in the following three groups: - Contiguity functions - Proximity functions - Spread functions
  • 65.
    Connectivity functions Contiguity functions •Contiguity functions are usually applied to identify contiguous areas with specific size and characteristics. • A contiguous area consists of a group of spatial features that share one or more specified characteristics and form a unit. • Definition of contiguous areas changes with applications. • Example of application: search for land units to be used as parks. - Include: forests, rivers and swamps - under these conditions: contiguous land unit must have a minimum area of 400 Km2 with no sections narrower than 10 Km for the forests and 5 km for the swamps.
  • 66.
    Forest Swamp River Fields Example of ContiguityAnalysis Land Cover Map Contiguous Areas Conditions for contiguity: Land cover types: forest, swamps and rivers Minimum area: 400 Km2 Minimum section: 10 Km for forest 5 Km for swamp
  • 67.
    Connectivity Functions Proximity Functions •Proximity functions measure the distance between features. • The most common measurement units are length and travel time. • Proximity functions require the definition of four parameters: 1. the target (e.g. a hospital, a road, a house) 2. a unit of measure (e.g. distance in meters, travel time in minutes) 3. a function to calculate proximity (e.g. Euclidean distance) 4. the area of interest. • A proximity analysis usually results in the generation of a buffer zone around one or more map elements.
  • 68.
    Proximity Functions • Examplesof proximity analyses are: - make a distance map from a given river within a watershed area by generating a buffer zone of increasing distances around the river (e.g. 0-250 m, 250-500 m, 500-1000 m, >1000 m). - define protected areas where building is not permitted around a wetland by generating a buffer zone of a specified width around the wetland. - analyze the pattern of noise propagation from an airport by calculating the distance of each location from the sound source and the expected rate of decrease in noise level with increasing distance.
  • 69.
    Example of bufferzone generation River 0 - 250 m 250 - 500 m
  • 70.
    Connectivity Functions Spread Functions •Spread functions evaluate phenomena that spread or accumulate with distance. • The output map is also called accumulation or friction surface. • A spread operation can be thought of as moving step-by-step outward in all directions from one or more starting points and calculating a variable at each successive step.
  • 71.
    Example of applicationusing a spread function • Spread function results can be presented as contour maps. In this figure: contours represent distances in Km away from starting point A. The shortest distance between A and B is indicated by the straight line connecting them. In this simple case spread and proximity functions are the same. A B + 1 2 3 4 5 6 7
  • 72.
    A B + 1 2 34 5 6 7 Absolute Barrier Example of application using a spread function In the case of an absolute barrier, such as a lake that obstacles truck travel, the shortest travel distance has to take into account the obstacle (red line). This type of analysis involving obstacles can not be accommodated by proximity functions.
  • 73.
    Examples of Applicationsusing spread functions • Transportation time and cost from and to selected features (e.g. railways, roads, mines). • Monitoring the spreading of pollution. • Mapping flooded areas. • Terrain trafficability: it is a complex analysis often used in military operations. The trafficability (or easy and speed of movement) depends on many variables such as: topography, land cover type, transportation and season.