I am trying to use two different layers together to generate a layer of random points that represent sample sites. The two layers are:

  1. A grid layer of hexagon-shaped polygons created using the [Create Hexagon Tessellation][1] tool.
  2. A polygon layer with four categories of percent impervious surface (%IS), created by reclassifying the NLCD %IS raster layer and converting to a vector polygon layer. Let's say the categories are 0-25%, 25-50%, 50-75%, and 75-100%.

I would like to generate 25 random points for each category of %IS (100 points total), but only one point per hexagon. So 25 hexagons that have a point placed within a %IS polygon representing 0-25%, 25 hexagons that have a point placed within a %IS polygon representing 25-50%, etc.

I have tried using the built-in Create Random Points tool, the [GME Generate Stratified Random Points tool][1], and the Sampling Design Tool. However, I have only been able to create either

  1. a points layer with one random point inside each hexagon but not associated with the %IS information (Create Random Points), or

  2. a points layer where the points are stratified correctly by %IS but not constrained by the hexagon layer (GME, Sampling Design Tool).

Is there a way to do what I'm attempting?

Here's an example of what a small portion looks like. The colors of the %IS polygon layer represent the four different classes (increasing %IS from blue to red).

Example image

  • Raster 2 polygon. Union with imp.polygons. dissolve using hex and imp. Multipart ok. Generate 25 – FelixIP Dec 6 '15 at 18:33
  • Unfortunately when I tried this process it still generates more than one point per hexagon. Thank you for the suggestion though. – michael Dec 6 '15 at 20:17
  • Will generate 1 work? – FelixIP Dec 6 '15 at 20:58
  • Clarifying: the hexagons are smaller than the IS polys? Can you provide an image of how they layout overlapped, hexagons and IS polys? And in your product, some hexagon will have a point and some won't, right? – Paulo Raposo Dec 6 '15 at 22:23
  • Paulo - the hexagons are larger than the IS polygons. I added an image to the original post. You are correct, some hexagons will have a point and some won't (which is fine). – michael Dec 7 '15 at 2:58

Raster 2 polygon. Intersect with impervious polygons. Dissolve using hex polygon ID and impervious class, multipart=Ok. Picture shows hexagons over impervious layer, note hexagons labels = their FIDs:

enter image description here

Add field SORT to dissolved table and populate it using rnd()*n, where n= count of records in dissolved table:

enter image description here

  1. Set definition query CLASS=1, sort it by field SORT and populate field INCREMENT with auto-increment by 1

enter image description here

  1. Select 1st 25 and create random points using field COUNT=1 and selected polygons as constraining extent. Result:

enter image description here

Goto step 1 and do the same thing for CLASS 2 etc

  • Wow Felix, thank you for taking the time to write such a complete answer. I tried it on one class and it worked, so hopefully I won't have any issues with the other three classes. The only thing that didn't work for me was the autoIncrement: I found python code (geonet.esri.com/thread/7502) and tried using it in the field calculator but it gave me a list of nonsequential numbers. I think it may have something to do with how the data was sorted but I'm not sure. My work-around was just to manually enter the incremental values (a bit tedious but it works). Thanks again! – michael Dec 8 '15 at 15:50
  • Use sort tool to sort records permanently. See advanced field calcs in arcgis help for autoincrement – FelixIP Dec 8 '15 at 18:01

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