introduction to cartographyrahat.sudburyweb.com/files/introductiontocartography_lecture7.pdf ·...
TRANSCRIPT
What is GIS?
• GIS is a system for– capturing,– storing,– retrieving,– analyzing and– displayinggeographic data.
GIS Concept• Use databases to keep spatial data and their
attributes so that analyses could be performed.
ESRI 2004
GIS Software
Personal Computer Workstation
Mainly Vector-Based ArcGISArcViewGeoMediaMapInfoPAMAP/TerraSoft
ArcInfoIntergraphMicrostationGRASS
Mainly Raster-Based IDRISIERDAS ImagineENVIGRASS
ERDAS ImagineENVIGRASS
ArcGIS• Developed by ESRI (Environmental Systems Research
Institute).• Components: ArcMap, ArcScene, ArcCatalog, ArcInfo
Spatial Data Structures in GIS
Vector
• Points
• Lines
• Polygons
Raster
• Points
• Lines
• Polygons
• Surfaces
Data Structures – Points
Examples
• Owl locations• Wildlife observations• Inventory plot locations• Homes• Archeological features•••
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Data Structures – Lines
Examples
• Roads• Streams• Contour lines• Logging trails / corridors• Cruise lines• Trails•••
Data Structures – Polygons
Examples
• Stands (management units)• Soils• Ownership boundaries• Lakes•••
Vector Data StructuresAdvantages and Disadvantages
• Advantages– Highly precise.– Compact data structure. Requires less storage space in
computer memory.– Closely approximates hand-drawn maps.
• Disadvantages– More complex than raster data structure.– Overlay operations are more difficult to process.– Representing a high-level of spatial variation is
difficult.
Raster Data Structures – Grid Cells
Examples
• Spectral reflectance (image)• Other EM radiation (thermal)• Classified data• Rasterized vector data• Digital elevation models• Scanned data
Raster Data StructuresLinear Features
• Raster representation of linear features has inherent error.
Raster Data StructuresAdvantages and Disadvantages
• Advantages– Simple data structure.– Computationally efficient.– Overlay operations are easy to process.– Representing a high-level of spatial variation is easy.
• Disadvantages– Topological relationships are difficult to understand.– Less compact – requires large storage space.– Display may not be visually appealing.
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.
Metadata
A description of an accompanying spatial data file.
Should include information about:
• When created• Who created• Minimum Mapping Unit (MMU)• Projection / Datum / Coordinate system• Attribute information• Accuracy Assessment• Maintenance policy• Source location• Copyright information• Contact
GIS Database Errors
These 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 locations
2) Boundary errors - uncertainty in the location of edges of features
3) Classification errors - features are not identified correctly
Classification Errors
Typing errors (recent harvest)
Vegetation classification (incorrect vegetation type)
Remember: All image classifications have error.