topic Re: Finding contiguous parcels based on area? in Spatial Data Science Questions

Finding contiguous parcels based on area?

AlmazNaizghi — Mon, 30 Mar 2015 15:13:32 GMT

I have one question which requires answer by performing GIS
analysis. There are more than 300,000 parcels for the city I am working. I need
to know 5 contiguous parcels each one has with an area of one acre for the entire
city. Then after finding those locations dissolve those 5 contiguous parcels to
one area (5 acres) for a development. What are the steps to follow and which
tools to use? I look forward your professional help.

Re: Finding contiguous parcels based on area?

XanderBakker — Mon, 30 Mar 2015 15:20:16 GMT

This would require to select by attribute your parcels of 1 acre (use a tolerance, since most likely hardly any will have an area of exactly 1 acre). Next Dissolve the parcels (don't create multiparts). In the resulting featureclass, those that have an area of 5 or more acres (apply the same tolerance) will be the ones that could be valid for the development.

In case you have dissolved polygons with an area over 5 acres, these will contain multiple solutions for 5 contiguous parcels.

Re: Finding contiguous parcels based on area?

AlmazNaizghi — Mon, 30 Mar 2015 17:48:09 GMT

Thank you Xander for your prompt reply.

I have tried by clipping small area. However, I am confused how and when to
use the tolerance for exporting the 1 acre parcels as well as when dissolving
to only 5 parcels.

Thanks,

Re: Finding contiguous parcels based on area?

XanderBakker — Mon, 30 Mar 2015 22:13:47 GMT

What I was trying to say is when you create a definition query to extract those parcels that have an area of 1 acre, you should not use area = 1 (if he unit is acres) but something along the line like:

area >= 0.99 and area <= 1.01

This will use a tolerance of 1 percent. Change this according to what you consider right. You can use the "Select Layer By Attribute tool".

Next step would be to use the "Dissolve tool". Dissolve all polygons (don't select any "Dissolve_Field(s)" and uncheck the option "Create multipart features").

The resulting featureclass can be used in the Select Layer by Attribute tool where you can select for areas larger than 5 acres. I assume you use featureclasses in a geodatabase (and not shapefiles). If you do use shapefile, you will have to add the area field yourself. See ArcGIS Help (10.2, 10.2.1, and 10.2.2) for help on that.

Once you have the remaining contiguous polygons (dissolved ones) you can start you development analysis for these locations.

Re: Finding contiguous parcels based on area?

AlmazNaizghi — Tue, 31 Mar 2015 15:59:47 GMT

Thank you for the detail explanation. I really appreciate it.

When I process small area as a sample. I have done the range to get the tolerance for exporting only around 1 acre parcels. The next problem I encountered was when I dissolve the resulting feature class doing the same step you stated, what I found was different result. For example if there are 10 contiguous parcels it dissolve them together and create 10 acres. My assumption was to limit only to 5 parcels. I think this needs some type of code which identify the 5 contiguous parcels and dissolve them if the criteria met. The good thing is I have discussed with my supervisor again and we agreed not to care about the resulting area as far as any contiguous parcels have dissolved. At this time I have processed and was able to figure out up to 3 acres, 3 to 5 acres, and more than 5 acres.

Thanks again!

Re: Finding contiguous parcels based on area?

XanderBakker — Wed, 01 Apr 2015 01:19:52 GMT

Indeed, what you found in the dissolved polygons that result larger than 5 acres, are those areas where multiple solutions of 5 contiguous parcels are located. To find all possibilities you would require some programming. This can be done, but at this point at least you have potential areas for development identified.

Let me know if in the feature you need this additional step, I can have a look how far we get with some Python programming.

Kind regards, Xander