13 Vector Data Structures Advantages and Disadvantages Highly precise.Compact data structure. Requires less storage space in computer memory.Closely approximates hand-drawn maps.DisadvantagesMore complex than raster data structure.Overlay operations are more difficult to process.Representing a high-level of spatial variation is difficult.
15 Raster Data Structures – Grid Cells ExamplesSpectral reflectance (image)Other EM radiation (thermal)Classified dataRasterized vector dataDigital elevation modelsScanned data
16 Raster Data Structures Linear Features Raster representation of linear features has inherent error.
17 Raster Data Structures Advantages and Disadvantages Simple data structure.Computationally efficient.Overlay operations are easy to process.Representing a high-level of spatial variation is easy.DisadvantagesTopological relationships are difficult to understand.Less compact – requires large storage space.Display may not be visually appealing.
18 GIS Databases General Characteristics Includes one spatial data structure (point, line, polygon, raster).Includes one thematic description.Includes an attribute table.A large GIS database may be a combination of several smaller databases.May or may not include metadata.
19 Metadata A description of an accompanying spatial data file. Should include information about:When createdWho createdMinimum Mapping Unit (MMU)Projection / Datum / Coordinate systemAttribute informationAccuracy AssessmentMaintenance policySource locationCopyright informationContact
20 GIS Database ErrorsThese errors can occur in GIS databases of either data structure (vector or raster):1) Positional errors - coordinates of a map feature differ from their true locations2) Boundary errors - uncertainty in the location of edges of features3) Classification errors - features are not identified correctly
21 Positional ErrorsProperty boundaryRoads v. Digital Orthophotograph
23 Classification Errors Typing errors (recent harvest)Vegetation classification (incorrect vegetation type)Remember: All image classifications have error.
24 GIS Terminologies Coverage Shapefile DEM TIN A GIS layer. Digital file format of ESRI’s ArcView software.DEMDigital Elevation Model in raster data format.TINDigital Elevation Model in vector data format.