Spatial Analysis (Vector I) Reading Assignment: Bolstad Chapter 9 (pp. 347-376)
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Transcript of Spatial Analysis (Vector I) Reading Assignment: Bolstad Chapter 9 (pp. 347-376)
Spatial Analysis (Vector I)
Reading Assignment: Bolstad Chapter 9 (pp. 347-376)
Questions about the physical world Planning:
• Conduct Research• Define Protocols
Collect/Create/Edit Spatial Data
Spatial AnalysisCreate OutputReport ResultsDecide and Act
Spatial Analysis
The output from a spatial operation may be spatial (i.e. a new data layer is produced.Or the output may be aspatial (e.g., a single value, or a table)
Geoprocessing Tools Perform a Spatial Operation
– Selection (select by attribute or by location)– Conversion between data models (e.g. vector to raster)– Buffering– Dissolving– Overlay
• Clip• Intersection• Union• Erase
Spatial Operations (examples):
Buffering
• Creates polygons around existing vector features• ArcToolbox -> Analysis -> Proximity -> Buffer
Fixed Distance Buffer
• Delineates an area a fixed distance from input features (same distance).
Variable Distance Buffer• Buffers at variable distances
Specified by a value in Att. Table.
Intersection
• The overlap between two polygons
Wikipedia
Union
• The combined area of two polygons
Esri does not use this for the term “union” Wikipedia
Dissolving
• Dissolves features in a layer together – Based on a common attribute value– Or all features together
• This is a proper Union
Dissolving:• Helpful in removing unneeded information • Prior to applying an area based selection• Example: Combine drainages for each river
Hydrologic UnitHydrologic Unit
Watershed Layer
Hydrologic Unit
Output of Dissolve on Hydrologic UnitOutput of Dissolve on Hydrologic Unit
Spatial Operation: Overlay
Combination of separate data layers to derive new information (a new layer).
Both spatial and (sometimes) attribute data are combined.
(Vector Overlay -- Vineyard)
SlopeSlope
StreamsBuffer
StreamsBuffer
Land Use
Land Use
SoilsSoils
Wetlands ranked according to their vulnerability to nutrient runoff.
Overlay Operations
• “Clips” one layer with all the features from another
Clip
Clip:
Clipping Trails Layer to Streams Buffer
Identify parts of trails that are within 50 Yards of a stream
Intersect
• Finds the intersection of features between two or more layers
Intersect
Case Study: Distribution of a Rare Fungal Species
Habitat Requirements: • Klamath Mixed Conifer • Annual precipitation > 50 in.
Goal: Find areas that meet these criteria(i.e., suitable habitat)
Erase
• Uses one layer to “erase” area from another layer
Erase
Case Study: Find Legal Grazing Land (Post Ordinance).
• New ordinance: No cattle grazing within 100m of a stream.• Find total amount of land where grazing would still be
permitted.
Split
• Splits up a layer into multiple layers based on the features in the second layer
Identity
• “Identify” the features in one layer that overlap with features in another layer
Symmetric Difference
• Finds the area of features that are in one of two layers and not in the other layers
Union
• Combines the features from one or more layers into a single layer. The resulting features are the unique areas between the two layers (not a true Union)
Update
• Appears to crop the features in one layer to avoid features in another layer:– I believe the help is wrong– Not sure what this would be used for
This is the actual area of the features from layer 1 (i.e. they are no longer rectangular)
Append & Merge
• Both these tools combine vector layers together without changing the spatial data.
• Append: Adds a vector layer into another EXISTING layer
• Merge: Combines multiple vector layers into a NEW layer
A problem in vector overlay:Multiple layers representing the same thing, or boundary line.
Example:
Layer 1: Incorporated areas
Layer 2: Unincorporated areas
The boundary differs,
but represents same
boundary on earth’s surface. Sliver Polygons
• Sliver Polygons– Take up space, but are not of any interest.– A significant increase in processing times. – Erroneous analysis results.
• Remedies– Set an X,Y tolerance when you perform your overlay operation.
• X,Y tolerance = a definition for the minimum tolerated distance between vertices
• Forces nodes or lines to be coincident if they are within the specified X,Y tolerance.
– Manually go through and remove sliver polygons – Dissolve – The “Eliminate” geoprocessing tool*.
• Merges selected polygon with neighboring polys with the largest shared border or area
*Requires an Advanced license.
Residential ZoningResidential Zoning Industrial ZoningIndustrial Zoning
ParcelParcel
Sliver PolygonSliver Polygon
Now called“X,Y Tolerance”
Union operation
With a 10 Ft X,Y ToleranceWithout an X,Y Tolerance