GIS2: Geo-processing and Metadata
Treg Christopher
Three Views of a GIS
• The Map View
• The Database View
• The Model View
Three Views of a GIS
• The Model View: – A GIS is a set of information
transformation tools (i.e. geoprocessing) that derive new data from existing data.
• What are the three types of vector data?
Geoprocessing using Vector Data
•Points, Lines, Polygons
Vector Data – Overlay Analysis• Union
– Spatial features and their attributes are joined to create a new layer
Vector Data – Overlay Analysis• Intersect
– Only the features that are common to both layers are combined to create a new layer
• Identity
Vector Data – Overlay Analysis
• Erase– Remove an areas from
the larger, geographic area
– Example: Where are endangered nesting areas where human activities aren’t allowed?
Proximity Analysis :Nearest Neighbor
Vector Data – Proximity Analysis
• Buffer:– find features contained
inside or that fall outside the specified distance.
– Points, lines, or polygons
– Different buffer distances
– Multiple bands
– Overlapped or dissolved zones
Proximity Analysis :Variable Width Buffering
Width of buffer varies by attribute value
Example: a buffer based on stream type and Timber BMP
Ephemeral - small or no buffer
Intermittent- 30ft
Perrenial-150ft
Vector Data – Feature Extraction
• Clip– Includes only those features
of the input theme that are within the areal extent of the clip theme.
– Isolate a particular area of interest.
– For aesthetics, storage space and processing time
– Input layer be point, line, or polygon features, but the clippinglayer (i.e., "cookie cutter") must be a polygon layer.
• Dissolve– Removes boundaries between
polygons that have the same value of a selected attribute.
– Reduces processing time, visual clutter, storage space
• Append– Add tiles together to create
one layer– Large datasets are often tiled
• Soils (by County)• Topos (by 7.5minute Quad)
Other geoprocesses
Geo-processing use Raster Data
• Square cells of equal size • Raster (grid) is well suited for computing
because: (1) grid cell have fixed locations, and• (2) grid can be treated as a two-dimensional
array;
Number of columns
Num
ber
of
colu
mns
Cell size
Examples? DEM, Satellite Imagery, Aerial Photo
Raster Data AnalysisMap Algebra
• Local Operation
Single grid
Raster Data Analysis Map Algebra
• Zonal Operation
Zonal Mean Example - Map Algebra
3333
3311
221 1
2211
Zone Grid
4431
6732
154 1
1221
Target Grid
4.174.174.174.17
4.174.172.172.17
2.252.252.172.17
2.252.252.172.17
Result
Three Views of a GIS
• The Database View: – A GIS is a unique kind of database of the world—a
geographic database (geodatabase). It is an "Information System” for Geography.
• Spatial Data
• Attribute Data
• Metadata
What is Metadata?• 1. What does the data describe?
– What is geographic area of the data?
– When was it collected?– what are the units of measure?
• 2. How reliable is the info?– How was the data generated,
processed, and modified? • 3. Who produced the data? What is the data
type?
• 4. What is the projection?• 5. What does each value in each
field of the table mean?• 6. How can I get it? Usage restrictions?• 7. Who wrote the metadata?
Example of Metadata at: http://www.vcgi.org/
Steps in GIS for Your Project
• Identifying the goals of the project
• Identifying the questions
• Choose the data
• Choose the tools to analyze the data
• Conduct the analysis and generate results
Example: Finding sites for creating new campground areas
• The goal– Find public places in Chittenden County that are suitable for low-level
development as campgrounds.• The questions
– What are environmental concerns for this development?• Water quality• Damage to vegetation
– What makes a campground suitable to the user?• Microclimate• Proximity
• The data– Environmental concerns
• Hydrology (streams, lakes), Wetlands, Areas of threatened species– Human concerns
• Slope, Aspect, Roads, Trails
The Tools
• Confine to Project Areas (Clip)
• Proximity to Features (Buffer)
• Remove Buffered Areas (Erase)
• Find areas of low slopes (Intersect)
ArcIMS Viewer for Chittenden
• Website at:
• http://ecovalue.uvm.edu/ArcIMS/Website/chittenden
End
• Questions?
Review Questions
• Geo-processing is a part of which of the 3 views of a GIS?• List and describe 4 types of overlay analyses• Be able to describe real life examples in which you would
use these• Describe “buffering” and give an example of it’s use • Describe “clipping” and give an example of it’s use• Be able to distinguish between examples of zonal, raster
processing and cell-by-cell, raster processing• What is metadata?• List and describe 4 of 7 elements of metadata