topic Merging two raster layers in Geoprocessing Questions

Merging two raster layers

COLINGUILFOYLE — Tue, 16 Feb 2021 14:54:45 GMT

Hi there,

I'm working on ArcGIS Pro and trying to combine two raster datasets - one contains five different rivers and the other shows land cover. I've been using the "Mosaic to New Raster" tool which works great - except since one river and one land class type have the same attribute value of 36, they are grouped together in the new raster when I need them to be categorized separately.

Any suggestions?

Re: Merging two raster layers

SteveLynch — Tue, 16 Feb 2021 15:10:44 GMT

try using Combine

Re: Merging two raster layers

COLINGUILFOYLE — Tue, 16 Feb 2021 16:15:50 GMT

I have tried Combine but only the rivers seem to display in the output, no land cover.

Re: Merging two raster layers

DanPatterson — Tue, 16 Feb 2021 17:15:10 GMT

Combine should produce a new raster with the unique combinations of the classes in both rasters.

If you want to see your "rivers" on top of your "land cover" then you will have to use

Con (Spatial Analyst)—ArcGIS Pro | Documentation

Now, hopefully your "rivers" layer is classed as "river" and "nodata" otherwise you will have to use SetNull to make it so.

Alternately, you can go back to the combine result and reclass the data so that any combination that contains "river" gets classes as such

Re: Merging two raster layers

COLINGUILFOYLE — Tue, 16 Feb 2021 17:48:24 GMT

I ended up merging them as polygons and then converting to rasters which seems to have worked well enough - I'm interested to know how you wanted me to use to Con tool however, but I wasn't able to follow your instructions, it may make sense if I show the attribute table.

Here is the attribute table from the combined rasters - each number under "RoadCORINE" represents a unique land use type, while each number under "RasterRiver_CopyRaster1" is a unique river. The output looks like below, where only rivers show (they should be surrounded by other land use types).

Hopefully this helps.

Re: Merging two raster layers

DanPatterson — Tue, 16 Feb 2021 18:39:25 GMT

what were the values surrounding the rivers? If they had a value other than nodata, you have to adjust for it in the con statement. Landcover isn't going to show through unless it is nodata on top

In pseudo code

Con("river", "river", "landcover") meaning if the river is data, then use river, if there is no data, then use landcover.

but if the area surround your rivers has a value of '0' and '0' isn't nodata, then all you will see is what was in the river layer. (in which case you could just add the layers together and the land would shine through, but your rivers would have a different class value)