Geoprocessing Overview and Operations

Geoprocessing Overview

• Geoprocessing transforms spatial objects, altering both geometry and attributes.
• Unlike spatial queries, it modifies spatial objects.
• Common modifications include creating/deleting features, altering size/shape, and physical cutting.

Key Questions for Geoprocessing Operations

• Does the operation change the geometry?
• Does the operation change the attributes?
• What is retained versus discarded in the process?

Types of Geoprocessing Operations

Overlay Operations

• These operations involve placing multiple spatial layers on top of one another to identify spatial relationships and extract new information.
• Requires at least two layers.

Clip

• Cuts a portion of the first input layer based on the shape of the second input layer ("cookie cutter").
• Resulting features retain the geometry within the clip boundary.
• Output attributes match input layer attributes without attributes from the clip layer.
• Example: Reducing a larger area to an area defined by another layer.

Erase

• Removes portions of the first input layer that overlap with the second input layer boundary.
• Remaining features have geometry outside the erase layer boundary.
• Output attributes match input layer attributes without attributes from the erase layer.

Union

• Combines overlapping and non-overlapping areas from multiple layers, creating polygons reflecting all combinations.
• Duplicates attributes in overlapping areas, potentially causing double-counting of features.

Intersect

• Retains only the areas common to all input layers.
• Output can be polygons, lines, or points, depending on input layers.
• Retains attributes from all input layers.

Identity

• Combines input layer geometry with attributes from an identity layer while preserving all input layer features.
• Maintains input layer geometry.
• Adds attributes from the identity layer in overlapping areas; assigns null values elsewhere.

Other Geoprocessing Operations

Merge

• Combines features from two or more input layers into a single layer.
• Attributes may be summarized or preserved depending on user specifications.

Dissolve

• Aggregates features based on specified attributes, resulting in larger features from smaller ones.
• Reduces the number of features (e.g., merging counties based on attributes).
• Summarizes attributes based on the aggregation process.

Buffer

• Creates a zone of specified width around a spatial feature (point, line, polygon).
• Output is a polygon layer, regardless of the input type.
• Can dissolve overlapping buffers to prevent double-counting.

Critical Questions for Geoprocessing Operations

• Is the geometry modified, and how?
• How many features are created or remain?
• Which attributes are included in the output?

Practical Considerations

• Area Calculations
• Careful handling of overlaps in buffers/unions to avoid overestimation if not dissolved
• Choosing the right tool (specific to goal)

Summary

• Geoprocessing is fundamental to spatial analysis in GIS.
• Overlays analyze spatial relationships (e.g., clip, erase, union).
• Other operations (e.g., merge, dissolve, buffer) modify geometry and attributes.
• Precise understanding of how these operations modify data leads to accurate spatial analyses.

Explore the fundamentals of geoprocessing, which involves transforming spatial objects by modifying their geometry and attributes. This quiz covers key questions, types of operations including overlay operations, and specific techniques like clipping. Test your understanding of how these processes alter spatial data.