How to create a risk map

Question asked by monicacgv on Oct 2, 2013
Latest reply on Jun 16, 2015 by sephefox
Hello all,

I have been working with this and after to try it 1 millions of times, I could not do it. I will explain:

I have to do a risk map of deforestation, so I would need to combine: map of risks from distances to roads (100km of distance, and risk values between 1 and 32), map of risk from distances to rivers(50 km of distance and risk values between 1 and 16), past deforestation map (risks value between 1-32 as a function of the density of deforested areas) and protected areas (risk value= 2). How can I do it?

I know that I must build each map and then combine all of them, but how?

Steps to take:

1. To create the map of risk from distances to roads and rails: first, buffer with 100 km of distance. Then I need to divide these 100 kms into 32 risk classes (each class with 3.125 km wide and 32 classes best represented the continuous field of risk from roads and rail), with areas closest fo the road/railway given highest risk (=32) and areas furthest away given lowest risk (=1).

I guess this is done with a buffer, but what kind? Euclidean distances, multiple ring buffer, normal  buffer... how?

2. To create the map of risk from rivers: I have to do the same procedure as before but with a distance of 50 km and risks between 1-16.

3. Now I should combine both maps, in order to obtain the risk from the two maps. I have done it with the sum of the raster calculator, but the thing is that I only get the common areas of both, and the rest disappears. How can I do this?

4. After that, I have to mix this result with the protected areas, so that everything that falls in a protected area will be reclassified as low risk (2).How?

5. And finally, I have to combine the last map with the deforestation density layer. This layer is divided into 32 classes based in the density values �??i.e. group of highest density values were given highest risk value (=32), and the group of the lowest density values were given lowest risk value (=1)... How now? I did it with raster calculator, but the same thing happens again, because It just gives me the common areas.

So, how can I do the preceding steps? and the final map? Any idea?

Thank you very much,

Monica