topic Re: Weighted overlay analysis in ArcMap Questions

Weighted overlay analysis

SuganeshA — Fri, 02 Jul 2021 07:49:31 GMT

Hello

I am using ArcMap for my M.Tech thesis project, which involves the process of weighted overlay analysis. I have created all the necessary criteria maps and reclassified them to a common scale i.e from 1-5 (1 being least suitable and 5 most suitable). The problem that I am facing is when I perform the Weighted Overlay Analysis the resulting map's legend is having only 4 values, whereas I need 5 values as my scale goes from 1-5, can anyone kindly help me with the issue? Kindly refer to the attached screenshot of the same. (The resulting map after the weighted overlay analysis i.e "uhi_suitability_new3" is having only 4 values, but the criteria maps in the table is having 5 values)

I'm quite new to GIS.

Thank you

Suganesh

Re: Weighted overlay analysis

JayantaPoddar — Fri, 02 Jul 2021 09:14:03 GMT

I think this is perfectly fine. You might not have any point (on the map) where the output Raster mean value is equal to 5.

Another way to check using Raster Calculator.

Let me consider there 3 input raster layers, viz., ras1, ras2 and ras3 with influence factor 24%, 55% and 21% respectively.

Expression

("ras1"*0.24)+("ras2"*0.55)+("ras3"*0.21)

What is the maximum value of the above output raster?

Re: Weighted overlay analysis

SuganeshA — Fri, 02 Jul 2021 12:19:57 GMT

Thank you for your reply.

I did the calculation as mentioned by you using the raster calculator as a result, I got an output raster with values from 1 to 4.34 (I have attached a screenshot for your reference)

So it is alright that the value is not present?

Thank you

Suganesh

Re: Weighted overlay analysis

DanPatterson — Fri, 02 Jul 2021 12:31:25 GMT

The values are converted to integer format in the first place (in both arcmap and Pro)

How Weighted Overlay works—ArcGIS Pro | Documentation

since it is a preference scale and the absolute values aren't used. You should follow the guidance in the help topic to set up the preference scale given the input ranges of you data.

Re: Weighted overlay analysis

JayantaPoddar — Fri, 02 Jul 2021 12:37:21 GMT

Absolutely. Had there been a value of 4.5 or more, that would have got rounded to 5.

You can also attach the Raster Calculator workflow in your dissertation to infer your result (since Weighted Overlay Analysis will give output Raster values in Integer).

You can further classify (symbology) the Raster resulted from Raster Calculator into desired number of classes. It depends on your ultimate goal.

Re: Weighted overlay analysis

SuganeshA — Fri, 02 Jul 2021 13:39:03 GMT

Thank you for your reply. Will look into it.

Re: Weighted overlay analysis

SuganeshA — Fri, 02 Jul 2021 13:40:09 GMT

Thank you for your reply, I will attach the raster workflow as advised by you.

Re: Weighted overlay analysis

AzeemSultan — Tue, 07 Jan 2025 16:59:55 GMT

Hello,

It seems like the issue you're facing might be due to how the weighted overlay tool handles the combination of values during the analysis process. Sometimes, when multiple layers are combined, certain value combinations might not appear in the final result if they don't have data overlap.

You can try checking the following:

Ensure that all your input layers cover the same extent and have matching cell sizes.
Verify that each reclassified layer indeed has all five values distributed across the area.
Check if any criteria layers have null or missing values in certain regions, which could reduce the final range of values.

For a detailed step-by-step guide on weighted overlay analysis in GIS, you might find this article helpful: Weighted Overlay Analysis in GIS.

Let me know if you need further assistance!