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spatial_analysis:settlements_and_landscape [2007/10/01 15:43]
steko
spatial_analysis:settlements_and_landscape [2007/10/08 17:37]
steko added polar diagrams
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-  - A raster DEM of the studied territory. You can obtain an aspect map from it +  - A raster DEM of the studied territory. You can obtain an aspect map from it using the ''​r.slope.aspect''​ module.
-    ​using the ''​r.slope.aspect''​ module.+
   - A vector map of sites or buildings dating from a defined period.   - A vector map of sites or buildings dating from a defined period.
  
 ===== The steps to the analysis ===== ===== The steps to the analysis =====
  
 +==== Preparing data ====
  
 Convert the vector map to raster with the command: Convert the vector map to raster with the command:
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 <​code>​g.region -p</​code>​ <​code>​g.region -p</​code>​
  
-Now the resulting raster map becomes our MASK:+Now the resulting raster map becomes our ''​MASK''​:
 <​code>​r.mask input=edifici.mask maskcats=*</​code>​ <​code>​r.mask input=edifici.mask maskcats=*</​code>​
  
-From now on, all subsequent operations will be limited to the cells defined in our MASK, corresponding to built+From now on, all subsequent operations will be limited to the cells defined in our ''​MASK''​, corresponding to built
 areas or settlements. areas or settlements.
  
 +If you need to remove the ''​MASK'',​ remember it a raster map like any other one:
 +<​code>​g.remove rast=MASK</​code>​
  
 +==== Histograms ====
 +
 +
 +The simplest analysis we can run is ''​d.histogram''​. These are the histograms of **elevation** and **aspect** for the whole of our study area. Aspect is calculated counterclockwise from east, thus 0 = 360 = E, 90 = N, 180 = W, 270 = S. See http://​grass.itc.it/​grass62/​manuals/​html62_user/​r.slope.aspect.html for the manual page of ''​r.slope.aspect''​.
 +
 +{{spatial_analysis:​nomask.elevation.jpg?​300|}}
 +{{spatial_analysis:​nomask.aspect.jpg?​300|}}
 +
 +Applying ''​built.areas''​ as ''​MASK''​ results in these histograms:
 +
 +{{spatial_analysis:​mask.elevation.jpg?​300|}}
 +{{spatial_analysis:​mask.aspect.jpg?​300|}}
 +
 +
 +==== Polar diagrams ====
 +
 +Aspect values are counted from 0 to 360 in degrees. So it would be better to plot aspect in a **polar diagram** instead of an histogram.
 +
 +The ''​d.polar''​ module does exactly what we need. Its complete documentation is at http://​grass.itc.it/​grass62/​manuals/​html62_user/​d.polar.html .
 +
 +It's handy to directly save the diagram to an EPS file for subsequent operations (inclusion in a LaTeX file, conversion to other graphic formats with ImageMagick,​ ...). Then you can use this command to get your diagram
 +<​code>​d.polar map=aspect.5m@PERMANENT undef=0 eps=all.eps</​code>​
 +These are the results:
 +
 +{{spatial_analysis:​nomask.aspect.polar.png?​300|}}
 +{{spatial_analysis:​mask.aspect.polar.png?​300|}}
 +
 +===== Results =====
 +
 +
 +This simple exploratory analysis leads us to understand that in the study area there'​s a strong preference for sites exposed S-SE, built mostly around 700 meters above sea level.
spatial_analysis/settlements_and_landscape.txt · Last modified: 2018/08/04 00:01 (external edit)