Ask A Cartographer

Creating a map of distances

April 06 2010 | 0 comments
Categories: Map Data

How do I create a map that shows areas that are closer to a stream than they are to a road? I know I need to use the spatial analysis tools but I am drawing a blank.

Mapping Center Answer:

Are you thinking of perhaps Euclidean Allocation? I tested this and it seemed to work.  I used trails and roads as inputs. This was my approach:

  1. I combined the trails and the roads into a single feature class (in the figure below, trails are black and roads are white) using the Append tool with the No Test option
  2. I added an attribute to designate which lines were roads and which were trails
  3. I used Euclidean Allocation to determine areas closer to trails (purple) versus areas closer to roads (green)

Euclidean Allocation

Note that you have to have the two things you are comparing in the same feature class -- you can create this appended feature class JUST for analysis and then delete it when you are done with it (it problably won't be much good for anything else.)  If you cannot put the two types of features you are comparing into the same feature class for some reason (e.g., they are different geometry types), write back because we have another idea for that situtation.

Additionally, note that this is EUCLIDEAN distance allocation -- it uses the straight line distance in Euclidean space (think of it "as the crow flies").  If you have to take a "cost surface" into account, you should use the Cost Allocation tool.  If you also have to take the terrain into acount, you should use Path Distance Allocation tool instead.

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