In the previous article, Tutorial : create an aptitude map with ArcMap, with and without fuzzy criteria (2) , we have started by preparing basic data ( criteria ) to build an aptitude map. Right now we will finish the work.
Ranking of the ground slopes with Spatial Analyst
To avoid steep slopes and look for areas where the construction ground is relatively flat, you must know the slope of the site to be searched. The Slope tool creates this type of map identifying for each cell the maximum rate of variation of the values of each cell relative to the neighbouring cells. To rank the map, use the Reclassification tool. Since it is better to locate the location on relatively flat terrain, set the 1 to sites with steep slopes and the value 10 to locations where the slope is more gentle. Then, classify the intermediate values linearly as shown in the following illustration.
We use the Reclassify tool from Spatial Analyst- toolbox> Sort.
- Open the Reclassification tool
- As layer in entry indicate Slope
- Accept the default value for the parameter reclassification field to use the Value field .
- Click Sort
- Set the Method to equal Interval (variable number) and the number of Classes out of 10.
- Click Reverse the news values.
The inversion of values applies new higher values with values that represent a slope less steep, since these surfaces are more suitable for building.
- Enter a name for the raster output parameter: PenteReclass
The result is the following:
Given the fact that the slope is a direct data from the field, unlike the two previous criteria (distances to schools and recreation centres), the distribution is clearly less regular.
Ranking of areas nearby the recreational installations using the fuzzy Criterion tool
However, classify the slopes in 10 classes between 0 and 75 ° does not really make sense with respect to construction constraints.
It is already known that in construction the limits are expressed in % of the slope and not in angle. Between 0 and 15% we are in the classical construction. Between 15 and 30% we are obliged to use the construction on piles or in scale. Beyond 30%, even if technically still feasible, the costs become prohibitive.
In our case, then, we can consider a terrain totally suitable for the construction of a school a ground having a slope between 0 and 15% (0 to 8.5 °) and totally unfit if the slope is >30% (16.75 °).
The result is as follows:
Ranking of land use with Spatial Analyst
To rank the map representing the types of land use, use the Reclassification tool. Since it is better to build on certain types of land use due to cost you must determine how to rank the values. The classification of distance values or slope is a procedure that remains quite simple. You must determine whether short or long distances are preferable and whether the steep or gentle slopes are desirable, then classify the rest of the values linearly or specify a distance or a maximum slope to take into account . Here you must determine the most appropriate types of land use. This process is subjective because it depends on your study. The simplest way is to decide which is best and which is the least appropriate. Then, rank in order of preference the types of use of the remaining soil. You have to continue with this process until all types of use are classified. Land uses such as water type and wetlands have been excluded from the analysis because you cannot build on water and must follow certain restrictions for the construction on wetlands. The illustration below indicates the classification of land use types.
Agriculture -> agricultural lands-> 10
Barren land -> arid lands-> 6
Brush / transitional -> shrub / transition zone -> 5
Forest -> forest -> 4
Built up -> built -> 3
Water -> water body -> 0
Wetlands -> wetlands -> 0
- Open reclassification tool (3)
- Accept the default value for the reclassification Field parameter to use the field LANDUSE
- Enter the values indicated for each type of occupation in the table
- click OK
The result is as follows:
Ranking of zones according to land occupation with the Criterion text tool.
The use of the command Criterion text follows the same process, the result is equivalent.
If we use seven levels of satisfaction, we will assign the following values:
Agriculture -> agricultural lands -> Excellent
Barren land -> arid lands-> Good
Brush / transitional -> shrub / transition zone -> Way
Forest -> forest -> Poor
Built up -> built -> Very bad
Water -> water body-> Excluded
Wetlands -> wetlands -> Excluded figura10
The result is as follows :
Well, we have finished with the preparation of different criteria that are needed to build the aptitude map.
In the next article we will discuss how to cross these criteria for obtaining the final result .