GIS data types – Vector Data• Points • Polygons • water supply wells • Lakes • Village centers • Village areas• Lines • Water lines • Road center
GIS data types – Raster Data• An array of cells• Represents continuous data layer• Best for data without easily defined boundaries• Each cell has one value
Comparison of 2 ways of representing GIS data Vector Raster
Vector Data Vector data provides a complex representation of the world it stores both: Attributes -- text or numerical information that describe the features (population of a village or number of orphans in a province) Geometry -- the shape or position of the features (boundary of a country or location of a hospital)
Attributes Nonspatial information about a geographic feature in a GIS Stored in a table and linked to the feature by a unique identifier For example, attributes of a river might include its name, length, and basin. Unique_ID River name Length_km Basin_km2 1 Mississippi 3,730 2,981,076 2 Amazon 6,937 7,050,000 3 Niger 4,180 2,117,700 17
Linking geometry and attributes • Unique identifier links geometry and attributes FID = 60 (Feature Identifier)
Shapefile data format (vector data) Actually, multiple files Attributes stored in dBASE table (.dbf file format) Shapefile.dbf table Hospital shapefile “Shape” field Access separate Coordinate file
Topology The arrangement that constrains how point, line, and polygon features in a vector data file share geometry. Topology defines and enforces data integrity rules (for example, there should be no gaps between polygons).
Raster Data: Images and grids Rows and columns of equally-sized cells Each cell stores a value Detail depends on cell sizeCan be stored in various image file formatsincluding: JPG, IMG, TIF, ASC, BMP, etc
Village-wise Slide Positivity Rate (M alaria) of Trans-Yamuna RegionRasters 2002 2004Images Data based grids Low High
Open Source GIS Software Diva GIS Dev-Info Health Mapper E2G QGIS others?
Open source GIS softwareSoftware NotesQGIS Easy to learn; training materials available; active user community writing modulesDIVA GIS Best suited for point data; limited data classification methods; robust point analysis capabilitiesDev-Info Mainly a data display tool, limited GIS capabilitiesHealth Mapper WHO mapping program; no planned updates; transitioning to DHIS- IIEPI Map Module in Epi-Info; limited GIS capabilities, best suited for Epi-Info users
Key Points GIS is an integration of 5 components GIS represents the world as layers Data can be stored as raster or vector There are standard features that should be present in a GIS: Storing, Querying, Displaying, Outputting DataAny questions?