topic Re: Setting Up a Grid for Random Sampling in Spatial Statistics Questions

Setting Up a Grid for Random Sampling

krystalphaneuf — Mon, 16 Jul 2012 16:29:24 GMT

We are going to go out in the field and map various areas that need to be excavated for biological surveying. We then want to place a grid over these areas and randomly select areas to excavate. Is there a way to place a grid over features and then randomly select say 30 sections within the grid to sample? I have all the extensions and have looked at the cartography, data management, and geostatistical analyst tools..

Thanks.

Re: Setting Up a Grid for Random Sampling

DanPatterson_Retired — Mon, 16 Jul 2012 17:08:41 GMT

Use the Fishnet tool
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//00170000002q000000
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/How_Create_Fishnet_works/001700000030000000/

then add a field to the output shapefile and calculate random integer sufficient to exceed the range of records you have and take the first 30
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//0017000000v8000000

Re: Setting Up a Grid for Random Sampling

KenBuja — Mon, 16 Jul 2012 18:47:45 GMT

Also take a look at the Sampling Desk Tool, available for both 9.3 and 10.

Re: Setting Up a Grid for Random Sampling

EricKrause — Mon, 16 Jul 2012 20:11:53 GMT

Once you have the fishnet polygons, you can use the Subset Features gp tool to get a random sample of a particular size.

Note: Subset Features will make a new feature class of the randomly sampled polygons. Depending what you want to do with the sample, this may be an advantage or a disadvantage of the tool.

Re: Setting Up a Grid for Random Sampling

krystalphaneuf — Wed, 18 Jul 2012 20:15:36 GMT

Thank you! I will try this and see how it goes.