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Theoretical help needed

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Hello all,

          Being a student in GIS, I have yet a lot to learn. I actually have to give in a report for my class, but there are two things I would like to do, that I am stuck on.

I am working on IDRISI Taïga. I have decided to map the natural risks of a town situated in a valley in order to find the places where the town can expand. I have now a map with the existing urbanized areas, the flood zones (where it is forbidden to build), the avalanche zones, the slopes under x% (from a DEM I made) and the roads (less than x meters from them - Buffer function). I am now left with zones that can potentially be urbanized.

First question: I have also mapped the forests: is it possible to favor the bare lands over the forests, and create a new class involving a cost factor? I would like to end up with a category of land that can be built for a certain price, and a second category that can be built but with a higher price because of the deforestation needed.

Second question: in the town planning documents, it is said that the minimum size for a plot is 130 sq meters. Is it possible to have the program calculate the maximum number of plots that can be implanted? If for example there is a piece of constructible land 1300sq meters, can I have the program to draw 10 plots on that area?

I hope I have been clear enough, pardon me for the mistakes as I am a "foreigner"  :smiley:

I hope you can bring me a bit more knowledge in a discipline I love so much.


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hem, first of all , Im not IDRISI user, so maybe my answer little bit general.

for first question, hum, if I'm not mistaken understanding your question, yes its possible, you can make the scoring in your land use map. for example you can add score 1 for land without deforestation and 2 that need deforestation. when you do analysis, like overlay, then you get the area with few score in sum for certain price and higher score for land that need deforestation. you can add weight score too, that will multiply the score if your variable is not at the same level that affecting your final variable

for second question , hum I still do not understand what plot is that ? plot of what ? town planning document , as far as I know in my country, only state the best land use for certain area. the government can control land use.

Uhm, to calculate maximum number of those plot that based on area, I think you can use calculate area on your map, and you can divide with your max plot area.

Im sorry for my language, since my native language is not english, and sorry IF Im wrong understanding your question

btw, I'm ArcGIS user, and for Remote Sensing, mainly I use ITTVIS ENVI, thats why I have few knowledge in IDRISI

regards, MOD

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Thanks for this first bit of advice. You have understood my two questions very well (good comprehension between two non-English natives!).

I will try an overlay (addition) in my macromodeller. However I don't understand the bit about "weight score" affecting the variable. I will try searching around for more information about that.

As for my second question, I was hoping (probably foolishly) that the program could make a vector file with 130 sq meter squares on top of my final raster. Finally I have done an "area" function to a text file and divided the results by 130 (explained in my written analysis). By plot I meant the number of plots of land that could be used for residential use.

Can you try and tell me more about the weight score if that is not asking too much?



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score, like 3dbu said, score is to make a grade or level on your variable, for example, as you mention before, for land use variable, you will make different grade for forest and bare land, so you fill different score for that.

and the weight score is how your variable affecting your process, for example, you have land use that already scored and you have other variable that affecting the land price like topography for example, then you will make decision based on local knowledge which one of that variable that affect higher in land price than the other, so you will assign different weight score for each variable, and the result is the score in each variable multiply by weight of the variable, thats all (this is very common task in Arcgis)

for your second question, I think its simple, you can use what I called in arcgis FISHNET, it will make square based on your setting, In Arcview, there is a bunch of extension that provide this task, maybe you can find standalone program, just search FISHNET

regards, MODERATOR

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