An overview of GIS data
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Transcript of An overview of GIS data
An overview of GIS data
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Today’s Topic:
• Data Types
• ArcGIS terminology
• Review of coordinate systems
• GIS Data Models
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2 basic types of Data Models• Raster• Vector
• Raster GIS• Vector GIS
Raster GIS• Raster is nothing but an array of grid cells• Each cell is called Pixel (Picture element)Example: IDRISI, ERDAS, GRASS
Pixel
Raster
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DEM (Digital Elevation Model):An example of Raster Data
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Raster representation of reservoir and highway
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Raster GIS• In Raster, each cell is
homogeneous • It represents either one class or
another, nothing in between• However, in reality, a cell is not
one thing or another.
Rasterizing of features
Mixel Pixel
Raster Data• Raster is good for
Continuous Data • Continuous Data: When data
varies smoothly across the area. Ex: elevation, precipitation, etc.
• Raster model provides the best representation for continuously changing data
Vector Data• Vector is good for Discrete
Data • Discrete Data: When data
value remain same for an area and then abruptly changes to another value.
• Ex: landuse, soils, etc.
Vector GISVector GIS is based on
POINTSLINES &POLYGONS
Example: ArcView, ArcGIS, Manifold, etc.
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Points Lines
Polygons
In the vector world everything is a point, a line, or a polygon
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Vector representation of reservoir and highway
GIS DataMost of the available GIS data have been developed using ARC/INFO
• Arc/INFO was a flagship product from ESRI
• It was widely used all over the world
Brief history of ESRI’s GIS software evolution
Software Data Format Year
Arc/Info Coverage 1980’s
ArcView Shapefile 1990’s
ArcGIS 8 & 9 Geodatabase 2000’s
ArcGIS 10 Geodatabase 2010
Spatial Data FormatArcGIS can work with spatial data in multiple formats• Shapefile• Coverage• Geodatabase
• Raster• CAD• Tables
Common data formatsShapefilesCoverages Geodatabase
Shapefiles
Shapefiles in Windows Explorer
Shapefiles in ArcCatalog
A shapefile consists of multiple files, and the common ones are *.dbf, *. shp, *.shx
2 types of Geodatabase• File geodatabase (soils.gdb-newer type)
• Personal geodatabase (soils.mdb-older type)
What can be in a Geodatabase• Feature datasets
- Collection of related feature classesFeature dataset
Feature classes
• Feature classes• Tables• Annotations• Rasters
Why Geodatabase?
It is not only a container of different types of data but also provide enhanced functionalities• Domains• Rules (split and merge policies)• Topological association
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Other types of dataTables
Layer file
- Does not contain data- But stores the symbology
Layer and Layer file?• A layer represents
geographic data displayed in ArcMap
• A layer references the data on a disk and keep it in
memory rather than storing the data
• A layer is created when you add a dataset to ArcMap
Layer and Layer file?• Layer is drawn with a default set
of drawing properties (symbology)• Layer can be saved to a file as a
layer file (.lyr) to store the symbology and shared with others
Map Documents
1. When you save a map in ArcMap, it will be saved as a file on disk called map document (.mxd)
3. Map documents make it easy to save, reuse, and share your work in ArcMap
2. Map documents (.mxd) do not store the data in it except the link to the data source
More on data• GIS data may be projected or unprojected• Projected or unprojected, GIS data is usually
attached to a coordinate system• How do you determine the coordinate
system of your data?
Two types of coordinate systemsGeographic coordinates:• Unprojected • Map units are in decimal degrees
Projected coordinates: • Data is projected • Map units are in feet or meters
Projected or Unprojected ?
Projected/Unprojected?
Projected Coordinate Systems (SPC)
How do you know the UTM zone of a place?