topic Re: Raster calculator won't add layers properly in ArcGIS Spatial Analyst Questions

Raster calculator won't add layers properly

psiri — Fri, 25 Jul 2014 16:26:26 GMT

Hi there,

I'm having some difficulty adding raster layers. I'm trying to create a species richness map and I was thinking of layering them via the calculator. The files I have are individual species distributions (which are just patches of 1 grids), and I have a main raster of the map of the location (which are patches of 0 grids). Now, when I add the layers on raster calculator (irrespective of order), I end up with just the patches of 1 and the larger map just disappears. This would still happen if the values were 1 and 2 respectively, the grid cells for the main map would just disappear anyway.

What I want is to still have those grids with the value 0 so it would be uniform for all the species so I would be able to overlay all of them at once and get a map of the richness. The size of the cells are the same, and they are under the same projection. I just dont know what might be the reason.

Does anyone know why this happens/what I can do about it?

Any help would be greatly appreciated. Thank you.

Siri

Re: Raster calculator won't add layers properly

DanPatterson_Retired — Fri, 25 Jul 2014 17:13:32 GMT

If there are areas of NoData in any of the grids, NoData will be returned, see the image here

Re: Raster calculator won't add layers properly

psiri — Fri, 25 Jul 2014 17:21:19 GMT

the values are 0. So technically they should still be carried forward but it doesn't.

Re: Raster calculator won't add layers properly

curtvprice — Fri, 25 Jul 2014 17:29:47 GMT

p, I suggest using the Cell Statistics tool with SUM option. That would run faster anyway. If you do have NoData issues there is a checkbox to ignore NoData in the SUM.

Re: Raster calculator won't add layers properly

psiri — Mon, 28 Jul 2014 11:40:03 GMT

Hi Curtis,

I've tried the cell statistics tool but I'm facing another problem I can't seem to figure out:

This is basically my file, the blue being the Madagascar area (grid size around 590,000) and pink being species distribution.

However when I use the cell stat sum tool: it produces this raster. I dont know where the green square is coming from?

Would you know why this is happening?

thank you

Siri

Re: Raster calculator won't add layers properly

psiri — Mon, 28 Jul 2014 12:22:28 GMT

Nevermind, I realised I didnt need the base raster afterall. So now its worked! Thank you!!