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Clustering creates pie charts that help illustrate patterns within large spreadsheet data sets.

There's virtually no end to the ways you can apply GIS mapping tools to visualize data and see trends and patterns that might not be detected in a spreadsheet alone.

While it's common to use dropped pins to view data-set types within a map, multiple overlapping pins make it difficult to detect meaningful patterns. That's why I use the clustering feature commonly included in many GIS mapping programs. Clustering generates simple pie charts that make it easier to discern patterns.

How does clustering work?

Say you need to visualize sale price to list price ratios for a given area. Follow these steps:

1. Create your spreadsheet making sure each listed property has the correct address and ZIP code. These two fields are required for accurately geo-referencing the spreadsheet data in a map.

2. Copy and paste your spreadsheet data into the designated section of a GIS program. BatchGeo is one of the GIS tools I use to convert spreadsheet data sets into a map, and it's the one I used to demonstrate this clustering example. It's surprisingly easy to use and free for mapping up to 250 properties. (Read my review of BatchGeo in the Q2 2011 issue of Valuation at

3. Select the Validate & Set Options feature and check the appropriate boxes to "enable clustering for high-density markers" and for "when clustering show the average of SP/LP."

4. Click the Make Map button. Your data will appear in a pie chart with percentages of change illustrated with different colors; a legend shows which color corresponds to which percentage.

A cluster of uses

The clustering feature can be used to model many different data points in a spreadsheet, including:

* Sale price by property type.

* Resale price change by month or from year to year.

* Capitalization rates by property type.

* Price per square foot.

* Year built by property type.

I've also used it to detect valuation patterns between properties in different locations, such as waterfront versus inland. > Find BatchGeo at

About the Author

John Cirincione, SRA, is chief appraiser for Collateral Analytics, which develops real estate analytics products and tools for appraisers, financial institutions, institutional and retail investors, and property capital market activities.

> Have a mapping tool or tip? Send suggestions to

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Title Annotation:Maps & Comps: Tips and tricks with mapping programs
Author:Cirincione, John
Publication:Valuation Magazine
Date:Jan 1, 2019
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