A problem with Map Algebra - 1+0+0 = 0?

Discussion created by mpschuuring on Apr 6, 2012
Hello everybody,

I'm a new user to ArcGIS and I'm using ArcGIS for my bachelor's thesis.

To summarize, I'd like to make a predictive model based on certain features in the landscape I've reclassified with a potential of '1' or '0' based on expectations of that feature. This I have done for three different raster maps, and I'd like to calculate these values of 1 (or 0) for each of these maps and combine them in a map where expectations can range from 0 (no expectations) to 3 (very high expectations).

When I'm using map algebra to do this however, I noticed certain areas which should have a value of 1, because one of the maps has a value of 1, shows a value of 0 - this is because the other two maps have a value of 0 in that area. Of course, it doesn't do this everywhere otherwise no area would have a value of 1. What is the problem here?

I'm sorry that this may be a stupid question, but it has been bothering me for quite a while - how do I fix this?

Thanks in advance!

P.S. Hopefully my expertly made paint-image clarifies the problem.