1. Vector Geoprocessing

2. Introduction to GIS
Geoprocessing
Geoprocessing is the processing of geographic information.
Perform spatial analysis and modeling via tools that transform datasets
Includes methods to automate GIS workflows

3. Geoprocessing Three general classes of tools
Introduction to GIS
Geoprocessing
Three general classes of tools
Breaking features into smaller features (e.g. Clip, Intersect, Union)
Aggregating features into larger features (e.g. Dissolve, Merge)
Creating new polygon features through buffering (e.g. Buffer)

4. Geoprocessing in ArcGIS
Introduction to GIS
Geoprocessing in ArcGIS
Perform geoprocessing in ArcGIS
Run a tool using its dialog box.
Run tools at a command line.
Build and run a model
Create and run a script

5. Geoprocessing in ArcGIS
Introduction to GIS
Geoprocessing in ArcGIS
Several ways to do this….
Run a tool using its dialog box.
Run tools at a command line.
Build and run a model
Create and run a script

6. Finding Geoprocessing Tools
Lecture 3b
Introduction to GIS
Finding Geoprocessing Tools

7. Vector Overlay Functions
Introduction to GIS
Vector Overlay Functions
Slide courtesy of Leslie Morrissey

8. Union Combines features of two or several themes
Introduction to GIS
Union
Combines features of two or several themes
Keeps all line work (extent contains both inputs)
Breaks down features, and creates new polygons
Keeps all attributes
Polygon only (no points/lines)
Image source: ESRI Arc Info electronic help

9. A list of Polygon datasets
Introduction to GIS
Tools: Union
Polygons only
A list of Polygon datasets

10. Intersect Yields areas that are common to both layers
Introduction to GIS
Intersect
Yields areas that are common to both layers
Preserves line work within common extent
Usually creates many new, smaller polygons
Preserves all attributes from both
Polygon overlaid with…
Polygon
Line (output: line)
Point (output: point)

11. Introduction to GIS
Tools: Intersect
Two layers

12. Union vs. Intersection Intersect: Union:
Introduction to GIS
Union vs. Intersection
Union is the complete combination of two overlapping sets of features and intersect is the intersection of inputs (only the overlapping parts)
Layer
Layer 2
Intersect:
“1 AND 2”
Union:
Layer 2
Layer
“1 OR 2”

13. Union vs. Intersection: Example
Introduction to GIS
Union vs. Intersection: Example
Here’s an example. Say we have deer wintering areas in one layer and conserved lands in another.

14. Union vs. Intersection: Example
Introduction to GIS
Union vs. Intersection: Example
Union gives us land that is EITHER conserved OR that is a deer wintering areas

15. Union vs. Intersection: Example
Introduction to GIS
Union vs. Intersection: Example
Intersect gives us land that is BOTH, and preserves all polygon boundaries within that common extent

16. Identity Identity performs a special type of intersection
Introduction to GIS
Identity
Identity performs a special type of intersection
Keeps all “input” features and attributes but only overlapping “identity” features and their attributes
First (“input”) layer determines geographic extent
Polygon with polygon, point, or line
Kept, as with union
Common (intersecting) areas
Not kept, as with intersect

17. Overlay trouble warning….
Introduction to GIS
Overlay trouble warning….
Output layer combines spatial polygons and attribute tables
Overlay
Parcels
Impervious/Pervious
Yikes!
Zillions of polygons!
Illustrative material courtesy of Leslie Morrissey

18. Overlay trouble warnings….
Introduction to GIS
Overlay trouble warnings….
Can result in polygon slivers Yikes!
Output file type (shapefile vs. feature class)
Shapefile output: no recalculation of area, perimeter, or length fields Double yikes!
Output as GDB feature class for accurate area, perimeter, and length calculations!
Input layers must have matching projection/datum (spatial reference)
No automatic recalculation of numeric attributes for polygons that depend on a spatial unit! More error!
Slide content courtesy of Leslie Morrissey

19. Overlay attribute errors
Introduction to GIS
Overlay attribute errors
All input layer attributes are preserved as is
Population is attributed to each output polygon
Count is not recalculated proportional to area
Total population for output is wrong!
States
Country
Output
Uh oh! A+ 9M B+ 9M A B +
Population
= 9 million = C D C+ 9M D+ 9M
Sum Pop. = 36M??
Slide content courtesy of Leslie Morrissey

20. Introduction to GIS
Clip
This uses one theme to “clip,” or serve as the outer boundary of another theme
Breaks down features into smaller units
Preserves the input theme’s attributes
Polygon only
Point, line, or polygon

21. Introduction to GIS
Tools: Clip
Point, line, polygon
Polygon

22. Clipping highways for Merced
Introduction to GIS
Clipping highways for Merced
Note that the “use selected features only” option was used

23. Introduction to GIS
Clipping roads

24. Dissolve Tool for aggregating polygons—making them bigger.
Introduction to GIS
Dissolve
Tool for aggregating polygons—making them bigger.
Single layer operation

25. Introduction to GIS
Tools: Dissolve

26. Dissolve: Example Dissolve zip codes (small) into counties (large)
Introduction to GIS
Dissolve: Example
Dissolve zip codes (small) into counties (large)

27. Introduction to GIS
Dissolve: Example
Choose the dissolve field: e.g. Dissolve based on the County field

28. Introduction to GIS
Dissolve : Example
Summarize the resulting field values. For instance, you could sum population for each county, or average size of ZIP code zones for each county

29. Introduction to GIS
Dissolve : Example
Now we have created a county map, and for each county we have an attribute containing the sum of population of the constituent zip codes

30. Introduction to GIS
Merge
Allows you to “join” two adjacent or non-adjacent themes into the same layer
Like “tiling”
Best when attributes match

31. Introduction to GIS
Tool: Merge

32. Merge Often when you merge you will want to follow up by dissolving.
Introduction to GIS
Merge
Often when you merge you will want to follow up by dissolving.

33. Introduction to GIS
Tools: Buffering
Buffering is when you draw a polygon around a feature (point, line or polygon)

34. Tools: Buffering Based on distance Based on attribute
Introduction to GIS
Tools: Buffering
Based on distance
Based on attribute

35. Tools:Variable Width Buffering
Introduction to GIS
Tools:Variable Width Buffering

36. More Overlay Tools Erase – remove some interior portion of a layer
Introduction to GIS
More Overlay Tools
Erase – remove some interior portion of a layer
Update – merge new features, e.g., add new parcel to parcels layer
Some content courtesy of Leslie Morrissey

37. Combining Geoprocessing Tools
Introduction to GIS
Combining Geoprocessing Tools
Involve multiple tasks performed in sequence, such as those that clip, buffer, intersect, union, then select datasets.
Step by step
Build and run a model
Create and run a script

38. Combining Buffering and Geoprocessing: Example
Introduction to GIS
Combining Buffering and Geoprocessing: Example
Question: How to find areas that are near deer wintering areas and water bodies but far from traffic?
Geospatial Data
Polygon layer for deer wintering areas
Polygon layer for Water bodies
Roads layer: line features

39. Combining Buffering and Geoprocessing: Example
Introduction to GIS
Combining Buffering and Geoprocessing: Example
Question: How to find areas that are near deer wintering areas and water bodies but far from traffic?
“Near” or “Far from”:
Buffering
Areas that are near deer wintering areas AND water bodies:
Intersect
Combining the layers:
Union
Selecting: Query for areas that are not within a traffic buffer

40. Combining Buffering and Geoprocessing: Example
Introduction to GIS
Combining Buffering and Geoprocessing: Example
Buffering: Made fixed buffers around deer wintering areas and water bodies, and a variable buffer around roads, based on traffic

41. Combining Buffering and Geoprocessing: Example
Introduction to GIS
Combining Buffering and Geoprocessing: Example
Intersecting: The intersection of deer wintering buffers and water buffers (the area in the red)

42. Combining Buffering and Geoprocessing: Example
Introduction to GIS
Combining Buffering and Geoprocessing: Example
The union of that intersection with the traffic buffer:

43. Combining Buffering and Geoprocessing: Example
Introduction to GIS
Combining Buffering and Geoprocessing: Example
Selecting: Query for polygons that are not within (far from) a traffic buffer

44. Combining Buffering and Geoprocessing: Example
Introduction to GIS
Combining Buffering and Geoprocessing: Example
Create a new layer by exporting the selected features (polygons)

45. Flow Chart for Analysis
Introduction to GIS
Flow Chart for Analysis
Deer wintering areas
Water
Traffic
Deer/water buffers away from roads
Export
Buffer
Buffer
Buffer
Deer/water buffers away from roads
Deer_buff
Water_buff
Traffic_buff
Select
Intersect
Union
Deer/water buffers plus traffic buffer
Deer wintering & water buffers

46. Geoprocessing Summary
Introduction to GIS
Geoprocessing Summary
Union
Intersect
Identity
Clip
Dissolve
Merge
Buffer