Optimizing Pairwise Intersection in ArcGIS: Tips for Efficient Geospatial Analysis

====================================================================================

When working with large datasets and multiple layers in Geographic Information System (GIS) software like Esri's ArcGIS, efficient spatial analysis techniques are crucial. One such technique is the pairwise intersection, which compares each feature within one layer to every other feature across another or multiple layers to identify areas of commonality.

However, new users often encounter challenges with this process due to limitations in default settings and a lack of understanding about how these tools actually function under the hood.

In this article, we'll dive into optimizing pairwise intersection using ArcGIS's Intersect tool by exploring its capabilities, pitfalls, and best practices for improving performance when dealing with large datasets or complex spatial relationships between features.

Understanding Pairwise Intersection

-----------------------------

Before diving into optimization techniques, it's essential to understand what the pairwise intersect operation actually does. In simple terms, given two layers (e.g., layer A and layer B), this process will:

1. Compare each feature in layer A with every other feature in layer B.

2. Output a new layer containing only those features that have at least partial overlap between them.

The Intersect Tool: What You Need to Know

--------------------------------

In ArcGIS, the primary tool for performing pairwise intersection is called 'Intersect.' While its name might suggest otherwise, this powerful function can actually handle any number of input layers and even perform complex spatial operations beyond simple feature-by-feature comparison.

To use the Interjoiner properly:

1. Open your project in either ArcMap or ArcGIS Pro.

2. Ensure both target (input) layer(s) are added to the table of contents (TOC).

3. Click on 'Analysis > Spatial Analyst Tools' from the main menu, then select 'Intersect.'

4. In the resulting dialog box:

* Under 'Input Features,' specify all layers you want to intersect.

* Choose your desired output location and name for the result under 'Output Feature Class.'

Optimizing Pairwise Intersection

------------------------------

Now that we've covered the basics of how pairwise intersection works in ArcGIS, let's move onto some practical tips for improving performance when dealing with large datasets or complex spatial relationships:

### Tip 1: Reduce Input Layer Size

The more features you're comparing across layers, the longer each individual comparison will take. Before running an intersect operation, try to reduce your input layer sizes by:

* Removing any unnecessary attributes using 'Fields > Delete'

* Simplifying feature geometries if possible (e.g., using 'Analysis > Spatial Analyst Tools > Dissolve')

### Tip 2: Utilize Efficient Join Types

By default, ArcGIS will perform an inner join when performing a pairwise intersect operation. However, depending on your specific requirements, other types such as left or right joins may be more efficient and still produce the desired results.

To change the join type:

1. In the 'Join Layer' dialog box:

* Under 'Join Type,' select either 'Left,' 'Right,' or 'Inner.'

2. Click OK to apply changes

### Tip 3: Leverage Spatial Indexing

Spatial indexing can significantly speed up pairwise intersection performance by allowing ArcGIS to quickly locate features that are likely to intersect without having to perform a full comparison.

To enable spatial indexing:

1. Right-click on the target layer(s) in the TOC and select 'Properties.'

2. In the resulting dialog box, click on the 'Indexing' tab.

3. Checkmark both boxes under 'Use Spatial Indexing.'

-------

In conclusion, optimizing pairwise intersection using ArcGIS's Intersect tool requires a combination of understanding how these tools function at their core, combined with practical tips and techniques for improving performance when working with large datasets or complex spatial relationships.

By applying the strategies outlined above - such as reducing input layer size, utilizing efficient join types, and leveraging spatial indexing - you can significantly speed up your pairwise intersection operations in ArcGIS and unlock more insights from your geospatial data. Happy mapping!

Intersect arcmap