Distance Map

A distance map is a proximity analysis type (distance measure among objects, usually as a length measure) presenting zones with specified width (distances) around one or more elements in the map, as presented in the figure below.

As an example, suppose one wants to bound all urban lots which are 50 meters far from a specified distance from a certain street. The purpose would be to know the city impact, when a dangerous material is transported through the city.

The next figure shows two possible paths to create a distance map, using as a reference elements like points, lines or polygons. Notice that it is possible to get a thematic raster map (which can be converted into a vector format later) by slicing a numeric IL with the distance grid representation, in this case the pixels will be grouped in slices associated to thematic classes. As another option, implemented since the version 3.6, it is possible to get a thematic map, however vector, defining the slices and the association with thematic classes previously defined in the database.

The difference between generating a distances numeric grid or a vector thematic map is in the output category selection, this is, numeric or thematic respectively.

The requirements for generating a distance map are the following:

  1. to identify over which representation the distance map will be executed (raster or vector)
  2. to identify the element (point, line or polygon), class or object that will be used to generate the output IL. The operation is valid for thematic, cadastral, networks or numeric ILs;
  3. to have a numeric category previously defined in the database, where the distances grid will be stored. And also have a thematic category, with enough number of classes to execute the grid slicing later;
  4. to have a thematic category, with enough number of classes to define the slicing, generating a vector representation IL directly.

Creating a distance map:

  • activate in the "Control Panel" the input information layer, thematic, cadastral, numeric or network, from which the distance map will be created;
  • select the IL representation you wish and draw in one of the windows;
  • select the IL in the main menu Thematic / Cadastral / DTM or Network - Buffering... depending on the model that the active IL belongs to;
  • in Selection, the buttons Class, Element or Objects will be enabled if:
    • the active IL is thematic:
      - Class: all elements of the selected class will be considered
      - Element: only the selected entity will be considered (Point, Line or Polygon)
      - select an option;
    • the active IL is cadastral:
      - Object: for all objects with the same label
      - Element: only the selected entity (Point, Line or Polygon)
      - select an option;
    • the active IL is network
      - Object: for all objects with the same label
      - Element: only the selected entity (Point, Line)
      - select an option;
    • the active IL is numeric
      - Element: only the selected entity (Point or Line)
      - select an option;
  • click in the screen over the desired entity. Each selection is presented in the Selected Elements list;
  • if you want to remove an entity, select an item in the Selected Elements list and click on Remove;
  • click on Category... to select a numeric category which will be used to store the IL with the distance grid or a thematic category that will be used to create the distance vector map. At this point the " Categories List" window is presented, select one in the list and click on Apply;
  • if the selected output category is numeric:
    • give the output IL name;
    • in Grid Resolution, give the grid resolution value in X and Y (meters);
  • if the selected output category is thematic:
    • give the output IL name;
    • in Distance Slices, click first on Definition... to inform the intervals for the distances slices. The "Slices Definition" window is presented. Click on Execute in this window after defining the slices;
    • in Distance Slices, click on Association... to make an association of the slices with thematic category classes selected. The "Slice - Classes" window is presented. Click on Apply in this window for the association;
    • type in Number of Points in the Curve: the desired value. Valid values between 1 and 180. This value corresponds to the number of points to be created in an 180 degrees curve. Curve with smaller angles will have a number of points proportional to this angle. If the distance slice increases it is recommended to increase the number of points in the curve;
  • click on Apply;

NOTE: Use resolution values smaller than the distance that will be defined later for the slicing. Once the grid is generated, with the distance values, go back to the "Control Panel", activate the IL that has the created grid above and click on the DTM - Slicing... in the main menu, to create a distances map.

See also:

Numerical Grids Slicing
Programming in LEGAL
Consulting a Database.


Other options in the SPRING geographical analysis