spatial database management and spatial reference system in GIS

1. Chapter 3
Database management systems
and Spatial referencing

2. Objectives of the chapter
After completed this unit, you will be able to:
 Describe Database management systems
 Describe Spatial Databases Management
 Explain Coordinate systems and map projections
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3. 3
Database management systems
Introduction:
A large, computerized collection of structured data is what we
call a database.
These applications have in common that the amount of data is
usually quite large, but that the data itself has a simple and
regular structure.
consider carefully what the database purpose is, and who will
be its users, Identify the available data sources and define the
format.
This format is usually called the database structure.
A database management system (DBMS) is a software package
that allows the user to set up, use and maintain a database

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Like A GIS allows to set up a GIS application, a DBMS offers
generic functionality for database organization and data handling.
• GIS database comprises spatial or entity or graphical database,
nonspatial or attribute database and a linkage mechanism for
their topology to show the relationship between the spatial data
attribute data for further analysis.
 Nonspatial (attribute) data can be stored in any conventional
data bases,
 whereas spatial data , which is the dominant data in GIS, should
have the data base which is capable for handling spatial data.

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Spatial Databases Management
The real world is too complex for our immediate and direct
understanding
We create "models" of reality that are intended to have some similarity
with selected aspects of the real world.
Databases are created from these "models" as a fundamental step in
coming to know the nature and status of that reality.

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A dataset: a homogeneous collection of data normally describing a
single kind of phenomenon
A database can be thought of as an integrated set of data on a
particular subject. (It is a collection of tables)
Spatial/ Geographic database is simply databases containing
geographic data for a particular area and subject.
Spatial database has a geometry data type

7. Geographic database tables are distinguished from non-geographic tables by
the presence of a geometry column (often called the shape column).
Geometry Column
No Geographic column
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GIS and databases
GIS -----which compiles, stores, manipulates, analyses,
models and visualizes spatial data, to solve planning and
management problems” (Christiansen, 1998 )
Database like a GIS, is a software package capable of
storing and manipulating data
Database is good for
storing large quantities of data,
multiple users at the same time,
data integrity
system crash recovery and
easy to use data manipulation language.

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Cont...
GIS is operate on more of in spatial data, and allows all sorts of analysis
that are inherently geographic in nature.
GIS---combine in various ways for the representations of geographic
phenomena
It has an embedded ‘understanding’ of geographic space and equipment
for efficient map production
Databases mostly lack this type of understanding.
GIS lack full-fledged query language to operate on tabular data
Databases is used for handling tabular data

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Cont...
The two, however, are growing towards each other
Databases, likewise, have moved towards GIS and many of
them
Now adays allow storing spatial data also in different ways.
The DBMS approach to storing geographic data offers a
number of advantages and disadvantages over traditional
file based datasets

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Advantages of DBMS
Eliminate/reduces redundancy.
Maintenance costs decrease
Multiple applications
Data sharing b/n managers and users and or customers.
Security and standards
Managing large amounts of data
Manipulating the database
Querying the database to retrieve specific data.
Updating the database (changing values).
Control

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Disadvantages
The cost of acquiring DBMS software can be quite high.
 A DBMS adds complexity to the problem of managing
data, especially in small projects.
For ‘small’ data sets:
Spread sheets,
Text files
Or even hardcopies

13. Generally speaking, a DBMS :
 Supports the storage and manipulation of very large data sets
 Can be instructed to guard over data correctness
 Support the concurrent use of the same data set by many users
 Provides a high-level, declarative query languages
 Supports the use of data model
 Includes data backup and recovery functions to ensure data
availability at all times
 Allows the control of data redundancy
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14. Terminology in spatial databases
The main terms are: geographic object, theme and map.
1. Geographic Objects:
The major objects to be considered at a conceptual level are
geographic objects.
 A geographic object corresponds to an entity of the real world and
has two components.
i. Description
ii. Spatial component
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15. 2. Theme
A theme is a collection of geographic objects. :
In a GIS, the geospatial information corresponding to a particular topic is gathered in
a theme.
Rivers, cities, and countries are examples of themes
A theme is hence a set of homogeneous geographic objects (i.e., objects having the
same structure or type).
3.Maps
When a theme is displayed on paper or on-screen, what the user sees is a map as it is
commonly displayed, with colours, a particular scale, a legend, and so on.
Topographic maps, railway maps, and weather maps are examples of maps
commonly used.
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16. Entities- Rows
Attribute- Column
Attribute value
Spatial Database components
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17. Characteristics of Spatial database
A spatial database is characterized by the following:
Contemporaneous - should contain information of the same season for
all its measured variables
As detailed as necessary for the intended applications
 Positionally accurate
Exactly compatible with other information that may be overlain with it
Internally accurate, describe the nature of phenomena without
significant error
Readily updated on a regular schedule
Accessible to whoever needs it
Spatial Data Integrity
Spatial Data Indexing and Access Method
Long Transaction Management
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Concept and types of Coordinate Systems
What is Coordinate System?
A coordinate system is a method for identifying the
location of a point on the earth.
Coordinate System is a means for identifying the location of
a point on a spherical or planimetric map.
Type of Coordinate System
1. Geographic coordinates
2. Projected coordinates

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Geographic/spherical grid coordinate system
It uses a 3D spherical surface to define locations on the earth.
The spherical grid system uses simple geometry and sets two sets of imaginary
lines (Parallels and Meridians) around the earth.
With this system we can then describe the locations of any of the objects we
wish to describe.
The position of any point is defined by the intersection of both imaginary lines.
PARALLELS circle the globe from east to west (Latitude)
MERIDIANS are drawn from pole to pole (Longitude)

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Cont... A: PARALLELS
B: MERIDIANS

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Cont...

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X represents the Longitude coordinate and
Y represents the Latitude coordinates

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Cont...
Latitude and longitude are measured in degree, minutes
and seconds.
 1 full circle= 360° (degrees)
 1° = 60' (minutes)
 1' = 60" (seconds)
For example:
The latitude 41° 27 minutes (‘) and 41 seconds (‘‘) north
=(41° 27´ 41´´N)
To transfer geographic coordinates into decimal degrees
you can use the following calculation:
• Decimal degrees = Degrees + Minutes/60 +
Seconds/3600

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Projected or Cartesian Coordinate System
Reference systems, called rectangular coordinates or
plane coordinates, allow us to locate objects correctly on
flat maps (Two-dimensional 2D maps projected from
reference globe)
The basic rectangular coordinate system consists of two
lines: Abscissa (X-coordinates) & Ordinate (Y-
coordinates):

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Cont...
Together the X and Y coordinates allow us to locate any
point or feature by combining the values of X and Y.
By tradition, when reading maps using rectangular
coordinates, we give the X value first and the Y value
second.

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Map Projection
A map projection is a method for mapping spatial
patterns on a curved surface (the Earth’s surface) to a flat
surface
It is is a mathematical model for conversion of locations
from a 3D earth surface to a 2D map representation.
Representing the earth’s surface in 2D causes distortion
in the shape, area, distance, or direction of the data

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Cont...
It is the orderly transfer of positions of places on the
surface of the earth to corresponding points on a flat
map.
Is the systematic arrangement of the earth’s parallels
and meridians onto a plane surface.
Uses mathematical formulas to relate spherical
coordinates on the globe to flat, planar coordinates.

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Map Projection - the transformation of a
curved earth to a flat map (3D to 2D)
Parallels and meridians used as a base on
which to draw a map on a flat surface

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Why do we need a projection?
Creating maps
We must choose an appropriate projection for the map to
communicate effectively
Part of good cartographic design
Sharing/receiving geographic data
Along with datum, coordinate system, we must know the map
projection in which the data are stored.
Then we’re able to overlay maps from originally different projections

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Types of Map Projection
There are different types of map projection systems which
are appropriate for different areas and applications.

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(Azimutal) Planar or polar projection
Surface of globe is projected onto a plane tangent at
only one point
Used frequently at N or S pole
Usually only one hemisphere shown (centered on N or
S pole)
For example: Lambert Azimuthal Equal Area

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Conic projection
Analogous to wrapping a sheet of paper around the earth
in a cone
Normally shows just one semi-hemisphere in middle
latitudes.
Very popular for maps of East-West oriented land masses
Example: Lambert Conformal Conic

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Cylindrical projection
It corresponds to projecting the Earth's surface onto a
cylinder tangent to the equator.
Low distortion at equator, higher distortion approaching
poles
a good choice for use in equatorial and tropical regions,
e.g., Ecuador, Kenya, Ethiopia, Malaysia
For example: Mercator projection

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Distortions Caused by Map Projections
All projection types have distortions in:
Shape
Area
Distance
Direction
Angle
Hence no perfect map projection can be defined.
Therefore, a suitable projection to be selected by
considering the purpose of the map and properties of
projections