topic Re: Create Random Points in Geoprocessing Questions

Create Random Points

MahdiHassan_Nayebi — Wed, 30 Jul 2014 20:03:52 GMT

Hello there

I have a question, I wonder if anybody can help me with it here.

basically I want to create random points, but I have difficulties with the conditions I want it to be created.

1. I have a field for the number of points in each feature (COUNT)

2. I have a vector/raster with a value for weighting points distribution. (Weight)

I know that I can use "Create Random Points" and do the distribution based on a field, but as far as I know I have no control over their distribution. I wonder if I can do this NUMBER of random points created based on the field that I have and their DISTRIBUTION based on the value of the vector/raster that i have as their weight for distribution.

I hope somebody can help me with this

Thanks

Re: Create Random Points

DanPatterson_Retired — Wed, 30 Jul 2014 20:07:43 GMT

What type of method are you proposing to do this? There are few/no tools available that don't produce point distributions based upon a specific pattern (ie random, circular, grid, linear etc)

Re: Create Random Points

KenBuja — Wed, 30 Jul 2014 20:28:49 GMT

Take a look at the Sampling Design Tool addin for ArcGIS 10. You can create random point and select how many points will be allocated to each attribute in a specified field. This can be done proportionally (by area), equally, or manually.

Re: Create Random Points

MahdiHassan_Nayebi — Wed, 30 Jul 2014 20:50:17 GMT

Thanks Dan

the image actually shows the polygons with the values I want the points to be distributed based on (basically the more distance from service area the less probability of point density in the area)

In this image you can see the random points created based on the field (but completely random), i want their distribution be based on the value of the polygons. I used create random points for this part.

I hope this is clarifying my question better.

Thank you again

Re: Create Random Points

MahdiHassan_Nayebi — Wed, 30 Jul 2014 20:53:33 GMT

Thank you Ken

Actually I saw this earlier today but didn't get to play with it to see if it actually can do what I want or not. I will give it a go in an hour.

Only one question, do you get to introduce number of samples manually or it can read it from attributes? I am trying with a small region but the actual model will have big number of different points to be created.

Thanks again.

Re: Create Random Points

KenBuja — Wed, 30 Jul 2014 20:57:58 GMT

You can manually enter the number of points for each attribute, or you can import a table that contains that the number of points to be created for each attribute.

Re: Create Random Points

MahdiHassan_Nayebi — Fri, 01 Aug 2014 13:48:11 GMT

Thank you Ken

It seems to me that this can be the right tool for me to use, but it was throwing an error when I was trying to use it. At the time I have some problem with my network analysis, after that I will come to see if I can actually fix the issue.

It seems to me that the two stage random can be the solution in my case, but I am not sure. I should have an answer by tonight.

Please correct me if I am wrong.

I assume I can use a field/raster value as the weight for distribution of sample points and another field as the count of the actual points.

Re: Create Random Points

KenBuja — Fri, 01 Aug 2014 14:03:15 GMT

What was the error you were encountering?

Re: Create Random Points

MahdiHassan_Nayebi — Fri, 01 Aug 2014 15:48:46 GMT

Here is a screen shot of the error I get

Re: Create Random Points

KenBuja — Fri, 01 Aug 2014 16:11:10 GMT

What types of layers are you using in your mxd? I'm suspecting there's an unexpected layer type that is causing a problem. What's the background image you're using?

Re: Create Random Points

MahdiHassan_Nayebi — Fri, 01 Aug 2014 16:18:18 GMT

That is a polygon feature which contains the count of the points.

The background is a simple ESRI basemap,

Re: Create Random Points

KenBuja — Fri, 01 Aug 2014 16:23:32 GMT

If you remove the basemap, does it work properly?

Re: Create Random Points

MahdiHassan_Nayebi — Fri, 01 Aug 2014 16:34:41 GMT

No, still getting the same error. I did delete every other element except the polygon and the boundary.

btw I am using the 10.2.2 version. can there be a version compatibility issue?

Re: Create Random Points

KenBuja — Fri, 01 Aug 2014 19:24:30 GMT

I didn't see any issue when running this on ArcGIS 10.2.2.

Re: Create Random Points

MahdiHassan_Nayebi — Sat, 02 Aug 2014 16:18:23 GMT

Thanks Ken Buja‌

It seems that the issue was with the shp file I had, I did create everything from scratch again and it seems that the tool is working perfectly in what it says it does. Just couldn't figure out if it can do the job I need.

Basically there are three methods for sample point creation, Simple, Stratified and Two Stage. To me the Stratified one seems to be the most suitable, but please en light me, cause I can not find a way to implement the tool to get the result I want. The result to me seems exactly like create random points tool in ArcMap. There is no way I could figure out to actually distribute the points proportionally I mean spatially weighted.

Please correct me if I am wrong in any of these statements

Thanks Again

Re: Create Random Points

KenBuja — Mon, 04 Aug 2014 18:52:19 GMT

I may be misunderstanding how you'd like to distribute the points. The Stratified method allows you to specify how many points will be created in the polygons that have the attributes listed in the field you selected.

In the example I showed in the screenshot in my initial message, there would be 9 points allocated to all the polygons that have the attribute "Coral Reef and Colonized Hardbottom". If there are more than 9 of those polygons, then some polygons will not have a point placed within them.

The number of points that are allocated are initially is set by the number of point you put into the "Sample units to allocate" text box. These points will be allocated to each attribute either proportionally by the area of the polygons or equally by dividing the number of points by the number of unique attributes. You can also manually allocate these points by changing the numbers in the table.