How to digitize a topo-sheet with the help of free MapWindow GIS Software Created By MRINMOY MAJUMDER(BE,ME) www.mrinmoy.majumder.info www.solveinweb.net
How to digitize a topo-sheet with the help of free MapWindow GIS Software Created By MRINMOY MAJUMDER(BE,ME) www.mrinmoy.majumder.info www.solveinweb.net This semi-graphical tutorial will help you learn the steps involved in the digitization of a toposheet by a free GIS software : MapWindow
GIS,Coverage,DEM Coverage : In geographic information systems, a coverage is a mapping of one aspect of data in space. It represents a "domain" (the universe of extent) in terms of characteristics expressing a range of values. For example: a satellite image derived from remote sensing might record varying degrees of light pollution. Aerial photography, land cover data, and digital elevation models are all considered coverage data. DEM : A digital elevation model (DEM) is a digital representation of ground surface topography or terrain. It is also widely known as a digital terrain model (DTM). A DEM can be represented as a raster (a grid of squares) or as a triangular irregular network . DEMs are commonly built using remote sensing techniques, however, they may also be built from land surveying GIS : A geographic information system (GIS), also known as a geographical information system, is an information system for capturing, storing, analyzing, managing and presenting data which are spatially referenced (linked to location). An ASTER DEM
Shapefile & Grids Shapefile : A "shapefile" commonly refers to a collection of files with ".shp", ".shx", ".dbf", and other extensions on a common prefix name (e.g., "lakes.*"). The actual shapefile relates specifically to files with the ".shp" extension, however this file alone is incomplete for distribution, as the other supporting files are required. Shapefiles spatially describe geometries: points, polylines, and polygons. These, for example, could represent water wells, rivers, and lakes, respectively. Each item may also have attributes that describe the items, such as the name or temperature. GRID : In cartography, any network of parallel and perpendicular lines superimposed on a map and used for reference is collectively called as grid . These grids are usually referred to by the map projection or coordinate system they represent, such as Universal Transverse Mercator grid. A binary grid file along with binary data in a xyz file
TIN TIN : A triangulated irregular network (TIN) is a digital data structure used in a geographic information system (GIS) for the representation of a surface. A TIN is a vector based representation of the physical land surface or sea bottom, made up of irregularly distributed nodes and lines with three dimensional coordinates (x,y, and z) that are arranged in a network of nonoverlapping triangles. TINs are often derived from the elevation data of a rasterized digital elevation model (DEM). An advantage of using a TIN over a DEM in mapping and analysis is that the points of a TIN are distributed variably based on an algorithm that determines which points are most necessary to an accurate representation of the terrain. Data input is therefore flexible and fewer points need to be stored than in a DEM with regularly distributed points. While a TIN may be less suited than a DEM raster for certain kinds of GIS applications, such as analysis of a surface's slope and aspect, TINs have the advantage of being able to portray terrain in three dimensions . Three-dimensional visualizations are readily created by rendering of the triangular facets. In regions where there is little variation in surface height, the points may be widely spaced whereas in areas of more intense variation in height the point density is increased.
Vector & Raster RASTER : A raster data type is, in essence, any type of digital image. Anyone who is familiar with digital photography will recognize the pixel as the smallest individual unit of an image. A combination of these pixels will create an image, distinct from the commonly used scalable vector graphics which are the basis of the vector model. While a digital image is concerned with the output as representation of reality, in a photograph or art transferred to computer, the raster data type will reflect an abstraction of reality. Raster data type consists of rows and columns of cells, with each cell storing a single value. Raster data can be images (raster images) with each pixel (or cell) containing a color value. Additional values recorded for each cell may be a discrete value, such as land use, a continuous value, such as temperature, or a null value if no data is available. VECTOR : In a GIS, geographical features are often expressed as vectors, by considering those features as geometrical shapes. A Raster Image A Vector Image Comparison Vector Raster
Coordinate System GEOGRAPHIC COORDINATE SYSTEM A property ownership map and a soils map might show data at different scales. Map information in a GIS must be manipulated so that it registers, or fits, with information gathered from other maps. Before the digital data can be analyzed, they may have to undergo other manipulations—projection and coordinate conversions, for example—that integrate them into a GIS. The earth can be represented by various models, each of which may provide a different set of coordinates (e.g., latitude, longitude, elevation) for any given point on the earth's surface. The simplest model is to assume the earth is a perfect sphere. As more measurements of the earth have accumulated, the models of the earth have become more sophisticated and more accurate. In fact, there are models that apply to different areas of the earth to provide increased accuracy (e.g., North American Datum, 1927 - NAD27 - works well in North America, but not in Europe). Projection is a fundamental component of map making. A projection is a mathematical means of transferring information from a model of the Earth, which represents a three-dimensional curved surface, to a two-dimensional medium—paper or a computer screen. Different projections are used for different types of maps because each projection particularly suits certain uses. For example, a projection that accurately represents the shapes of the continents will distort their relative sizes. Since much of the information in a GIS comes from existing maps, a GIS uses the processing power of the computer to transform digital information, gathered from sources with different projections and/or different coordinate systems, to a common projection and coordinate system. For images, this process is called rectification.
Coordinate System PROJECTED COORDINATE SYSTEM A projected coordinate system is a flat, two-dimensional representation of the Earth. It is based on a sphere or spheroid geographic coordinate system, but it uses linear units of measure for coordinates, so that calculations of distance and 7 area are 7 easily done in terms of those same units. The latitude and longitude coordinates are converted to x, y coordinates on the flat projection. The x coordinate is usually the eastward direction of a point, and the y coordinate is usually the northward direction of a point. The center line that runs east and west is referred to as the x axis, and the center line that runs north and south is referred to as the y axis. The intersection of the x and y axes is the origin and usually has a coordinate of (0,0). The values above the x axis are positive, and the values below the x axis are negative. The lines parallel to the x axis are equidistant from each other. The values to the right of the y axis are positive, and the values to the left of the y axis are negative. The lines parallel to the y axis are equidistant. Mathematical formulas are used to convert a three-dimensional geographic coordinate system to a two-dimensional flat projected coordinate system. The transformation is referred to as a map projection. Map projections usually are classified by the projection surface used, such as conic, cylindrical, and planar surfaces. Depending on the projection used, different spatial properties will appear distorted. Projections are designed to minimize the distortion of one or two of the data's characteristics, yet the distance, area, shape, direction, or a combination of these properties might not be accurate representations of the data that is being modeled. There are several types of projections available. While most map projections attempt to preserve some accuracy of the spatial properties, there are others that attempt to minimize overall distortion instead, such as the Robinson projection. The most common types of map projections include:
Coordinate System Coordinate System used in GIS Geographic Coordinate System Projected Coordinate System Custom Projection Continental,County,Solar etc. Groups UTM,NAD etc. Groups Names like Everest,European etc. Names like EMPC,ETRS etc.
Other File Formats .shp — shape format; the feature geometry itself .shx — shape index format; a positional index of the feature geometry to allow seeking forwards and backwards quickly .dbf — attribute format; columnar attributes for each shape, in dBase III format In each of the .shp, .shx, and .dbf files, the shapes in each file correspond to each other in sequence. That is, the first record in the .shp file corresponds to the first record in the .shx and .dbf files, and so on. KML : KML is a file format used to display geographic data in an Earth browser , such as Google Earth, Google Maps, and Google Maps for mobile. KML uses a tag-based structure with nested elements and attributes and is based on the XML standard. GPS : The Global Positioning System (GPS) is a satellite-based navigation system made up of a network of 24 satellites placed into orbit by the U.S. Department of Defense. GPS was originally intended for military applications, but in the 1980s, the government made the system available for civilian use. GPS works in any weather conditions, anywhere in the world, 24 hours a day. There are no subscription fees or setup charges to use GPS. GPS satellites circle the earth twice a day in a very precise orbit and transmit signal information to earth. GPS receivers take this information and use triangulation to calculate the user's exact location. Essentially, the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received. The time difference tells the GPS receiver how far away the satellite is. Now, with distance measurements from a few more satellites, the receiver can determine the user's position and display it on the unit's electronic map. Geodatabase : A geo-database represents geographic features and attributes that are stored inside a Relational Database Management System (RDMS). There are two types of geodatabases - Personal and Enterprise. The personal geodatabase in fact is in the format of Microsoft ACCESS (.mdb); Enterprise geodatabases are hosted in server-based DBMS such as SQL Server, Oracle, or IBM DB2 .
Workflow of GIS Digitization Insert the image to digitize Activate the digitization tool Digitized lines, polygons and points will be saved as ‘Shapefiles ’ Data Representation Digitize lines (for Rivers, Roads, telephone lines etc.),polygons (for ponds, lakes etc.)& points (cities, stations etc.) available in the map and enter the relevant information that you want to represent later Insert the shape or grid file as a new layer Data stored in the shapefile can be retrieved and represented as maps Shape files can also be converted into Grid file or geo-database to represent contour or elevation or depth etc. topographic features
Use of Shapefile,Grid,DEM,TIN,Geo-database in GIS DIGITIZATION SHAPEFILE (VECTOR) GRIDFILE GEODATABASE DIGITIZED MAPS MAP SERVER/INTERACTIVE MAPS REMOTE SENSED IMAGES DEM TIN IMAGE PROCESSING MAP/TOPOSHEET
What is the use of GIS/IP Software like ArcINFO, IDRISI,ERDAS ?
GIS software : -
Helps in digitization of maps/topo-sheets
Helps to create interactive maps representing one or more information
coordinate systems etc. The workflow of the software is given below
Create a New Project Insert a new layer Can be a new image or a new shapefile or grid file or geo-database Insert Plugins from Plugins menu Digitize or Represent Data with the help of those plugins
MapWindow Toolbars : Top Menu File menu will enable you to : 1.Create New or Open an Earlier Project, 2.Save the project, 3.Change Settings, 4.Connect to a database, 5.Print the map Edit menu will enable you to : 1.Copy or Export the opened map, its scale, geo-referenced map 2.Preview the map with full extent or using the current view in the Preview panel View menu will enable you to : 1.Add,Remove or Clear Layers.The difference between Remove and Clear Layers is on clicking Clear Layer all the layers will be removed but Remove Layer will only remove the selected layer. 2.Set Map Scale or Show Floating Scale Bar. 3.Zoom In or Out, Return to previous or next zoom,zoom to full or map extents. 4.Bookmark a mapview in a specific zoom or show a bookmarked view. 5.Show Legends or Preview the map PlugIn menu will enable you to : Add PlugIns.PlugIns are group of tools aimed at specific objectives.For example the ‘Converters’ plugin will convert CSV files into shapefiles.In mapwindow you can import any number of plugins from the mapwindow websites or use your own scripts.To add a plugin one has to copy and paste the dll files of a plugin into a subfolder within the mapwindow folder. Some plugins will be included by default.
MapWindow Default PlugIns Converters PlugIn Converts a CSV file into a shapefile. Watershed Delineation Useful for hydrologist. Helps to delineate watershed from DEM files. Shapefile Editor PlugIn 1.Show or Unshow Vertices 2.Snap or Unsnap Vertices 3.Snap to all layers 4.Stay in Add mode while adding shape files. GIS Tools PlugIn Allows to edit or update vector (shapefiles),Raster (gridfile) and Image files 1.Add Projections,2.Merge,Demerge shape files, clip shape files with polygons, buffer, Export shape files into a newer one etc.,3.Create grid images, reformat grids, merge grids, georeference grids or images, generate contour files, change no data files
MapWindow Important Icons Add New Project Open Old Project Save the Project Print the Map Add New Layers or Remove/Clear All Layers Pan(move) the map Select a shape file within a layer.The layer must be active while selecting the shapefile Measure Distance between two points Measure Area by drawing a polygon Zoom in or out or to full extent
Other Icons Identifier i.e. click on any shapefile after selecting this icon to know the informations stored into that shape file Attribute table Measures the distance and area of the shape files under the selected layers. Create a new type of shape file.Often called as Shape file container Starts to create a shapefile Click to Remove Selected Shape file Merge two or more shapefiles of same type Move Vertices Add(+) or Remove(-) Vertices
Vertex is a local extreme point of curvature and more than one vertex is collectively known as vertices.
Vertex Shapefile Editor will help you to show/hide vertices of the shapefile or you can enforce your shapefile drawing to automatically catch the vertices of a previously drawn shapefile by the “Snap to Vertices” menu or to stay at an Add Mode so that you are not required to click “Add Shapefile” repetitively.
Map window has a GIS Tools Plugin from where you can edit Vector/Raster/Image files.
Assign projections to any images or rectify the image into a world coordinate or if wish to reproject a already geo-referenced image you can also do that with this option Assign projections to any shapefiles or merge them or create new shape file with some existing shapes etc. various operation related to shapefiles can be performed This menu is for Raster files like grids. You can add a coordinate system, merge grids, create grid formats etc.
Adding Coordinate System SETTING THE COORDINATE SYSTEM 1 2 3
Adding Coordinate System SETTING THE COORDINATE SYSTEM File > Settings > Project Projection > Category/Group/Name 1 Category > Geographic/Projected/Custom 2 Show Mismatch Warnings ? > Yes (will show Mismatch warning)/No (not show mismatch warning 3 Use Projection Info ? > Yes (project will use the projection for each file)/No (will not use the projection ) 4
Adding Image for Digitization Add the scanned image Click and name the shape file, choose the type of shape file as polygon Click and select the type of shape file you want to draw ADDING IMAGE FOR DIGITIZATION 1 2 3
Selecting Types of Shapefile Create line shape file for rivers, roads, telephone line etc. Create a polygon shape file for lakes, land use, big rivers etc. Create point shape file for cities, stations, post office, village etc. SELECTING TYPES OF SHAPEFILE
Selecting Types of Shapefile Point Shapefile will have different ids and different location reference (i.e. coordinates) SELECTING TYPES OF SHAPEFILE Polygon shapefiles have same id for all of its points and the first and last point of a polygon will always have the same location reference (i.e. coordinates) Line shapefiles have same id for all of its points and the first and last point of a line will always be different (i.e. coordinates) You can identify this difference if you open the attribute table and look at MWShape id field 1 2 3
Attribute Table The new shape files will be shown in the layer manager panel Various types of values can be added by right clicking and selecting Attribute Table. Any information stored in this table can be visualized or represented in the map. VIEWING THE CREATED SHAPEFILES IN LAYER MANAGER ADDING VALUES TO ATTRIBUTE TABLE The map legend will be look like the Layer manager and can be exported by Edit>Export >Legend whereas the entire map can be exported as a jpg/bmp image by Edit >Export > Map
Attribute Table To Add New Fields i.e. columns to the table : Edit > Add Field, Select the type,Give a name and specify the field size and Click Add to add the field You can also select a field and zoom to it by using View > Zoom to Selected Shapes You can use the “Selection” Menu to Query the table values or use the “Export Selected Shapes” menu to export the selected features(Remember : Shapefiles consist shapes which are also called features) 1 2
Label Setup 1 2 Field to Show in Label Change the colour and alignment of the label Prepend or Append to the Label Change the Font Scale of the label And/or turn on/off Label Collision Avoidance
Legend Editor Create line shape file for rivers,roads,telephone line etc. In Legend Editor window (select the shape file and click Properties) you can change the colour of the selected shape file; thickness of border of a polygon or thickness of a line shape file; transparency; vertex colour and size; line style; tool tip (when mouse is placed on the shape file the value of the file can be shown in the tool tip); legend picture (picture to be shown in the map legend) etc. CHANGING THE COLOUR,STYLE AND DIMENSION OF CREATED SHAPE FILE WITH PROPERTY > LEGEND EDITOR
Merge,Move or Remove Shapefile Merge Shapefiles Remove shapefiles Move shapefiles MERGE OR REMOVE SHAPEFILES
MEASURING DISTANCE Click to Activate the Measure Distance Tool Click on the points to measure distance See the result here (right click to stop measuring) 1 2 3
MEASURING AREA Draw a polygon to measure area Click to Activate the Measure Area Tool See the result here (right click to stop measuring) 1 2 3
Generally, lakes, fields, wetlands etc. is digitized by polygon shape file. This is done by clicking the borders of the land use. After the border is delineated double click to end the polygon. Right click on the shape file and open the Attribute table and put the necessary values.
Next step is to digitize the roads, rivers etc. This features can be represented by the line shapefile.
Create another new type of shapefile and go on clicking on the rivers first. Then create another same type of shapefile and digitize roads and so on. Right click on the mouse to finish creating the shape file.
SUMMARY EDIT PROPERTY/LEGEND EDITOR FOR COLOURING AND LABELING ADD IMAGE FOR DIGITIZATION EDIT OR/AND ADD FIELDS IN THE ATTRIBUTE TABLE CREATE APPROPRIATE TYPE OF SHAPEFILE AND DIGITIZE THE LINE,POLY AND POINT FEATURES STORE THE SHAPEFILE FOR USE IN OTHER PROJECTS CONVERT THE SHAPEFILES INTO GRID OR OTHER FORMATS FOR VARIOUS TYPES OF DATA REPRESENTATIONS SET PROJECTION SYSTEM
How to digitize a topo-sheet with the help of free MapWindow GIS Software Want to know the way you can digitize GPS Waypoints or image map or xyz files ? Want to know more about digitizing with MapWindow ? Purchase the Semigraphical Book created by the same author named as : Digitization For Beginners For more info : www.solveinweb.net