Jens Ammon
Randomized Testing Sites
This exercise demonstrates how to create a series of randomized locations and use geoprocessing tools to ensure they fall under certain criteria, such as land ownership rights and easy accessibility.
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The accompanying map book contains 50 field sties the BLM would use to collect vegetation data over the area of interest. The sites were generated randomly in order to represent an unbiased sample of the area. Each site is a 20 m diameter circular plot that falls on BLM-owned land, and is within 500 m of a low traffic road for easy site access. Each map page has a detailed 1:1,000 scale view of the site location and a wider 1:15,000 scale view to show site proximity to the adjacent roads.
Map Creation Process
An initial set of 1000 points was created with the Create Random Points tool, and then buffered into 20 m circular areas. An excessively large amount of initial points was used to ensure that plenty of sites would meet all the required criteria.
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Using the Select by Attribute and Select by Location tools, the initial set of sites was then reduced to those that are both fully within BLM land and within 500 m of a low speed limit road (proxy for low traffic). With all the remaining site locations now fulfilling the required criteria, 50 locations were randomly chosen using the Subset Features tool.
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Finally a series of 50 site maps with identical layouts was generated with the Map Series tool.