Introduction to Cartography GEOG 2016 E Lecture-7 Geographical Information System

What is GIS? GIS is a system for capturing, storing, retrieving, analyzing and displaying geographic 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 ArcGIS ArcView GeoMedia MapInfo PAMAP/TerraSoft ArcInfo Intergraph Microstation GRASS Mainly Raster-Based IDRISI ERDAS Imagine ENVI

ArcGIS Developed by ESRI (Environmental Systems Research Institute). Components: ArcMap, ArcScene, ArcCatalog, ArcInfo

MapInfo Developed by MapInfo Corporation.

GRASS Open-source software.

Spatial Data Structures in GIS Raster Points Lines Polygons Surfaces Vector Points Lines Polygons

Data Structures – Points Examples Owl locations Wildlife observations Inventory plot locations Homes Archeological features

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 Structures Points Lines Polygons

Vector Data Structures Advantages and Disadvantages 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

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 Structures Linear Features Raster representation of linear features has inherent error.

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. 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

Positional Errors Property boundary Roads v. Digital Orthophotograph

Boundary Errors Fuzzy boundaries (stands)

Classification Errors Typing errors (recent harvest) Vegetation classification (incorrect vegetation type) Remember: All image classifications have error.

GIS Terminologies Coverage Shapefile DEM TIN A GIS layer. Digital file format of ESRI’s ArcView software. DEM Digital Elevation Model in raster data format. TIN Digital Elevation Model in vector data format.