Map Overlays and Spatial Joins

Extraction functions

Combine fearures but do not combine tables. Includes clip and erase.

Overlay with attributes

Combine both the fearues and the tables. Includes intersect and union.

Map overlay

Combines two feature classes to create a new feature class containing information from both inputs. Both features and attribures may be combined.

Union overlay

Combines and keeps all features. 

Intersect overlay

Combines features and keeps what is common to both.

1. Combine features spatially, producing all possible new features

2. Combine attribute tables, bringing original values from each table and assigning to each new feature

3. New spatial data set is created with features and attribute table

Steps to overlay:

Overlay types

Intersect: keeps common areas

Union: keeps all areas

Questions for spatial Joins

1. What is the spatial relationship between the features?

2. How should multiple join features be handled?

3. How should features be retained or handled?

4. Are the input layers compatible?

5. What attributes from the join features are needed?