# Weighted overlay analysis

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07-02-2021 12:49 AM
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New Contributor II

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

2 Solutions

Accepted Solutions
MVP Esteemed Contributor

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?

Think Location
MVP Esteemed Contributor

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.

Think Location
6 Replies
MVP Esteemed Contributor

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?

Think Location
New Contributor II

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

MVP Esteemed Contributor

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.

... sort of retired...
New Contributor II

MVP Esteemed Contributor

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.

Think Location
New Contributor II