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Exercise 3990. Points 3, theme: Correspondence of Categorical Surfaces

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Pixel values in the file 5434PK.rst represent basic areal categories according to Estonian topographical base map.

File 5434muld.rst represents soil types in the same map sheet. The meaning of numerical codes can be found from corresponding rdc files.
  1. On which soil type lays the majority of forests (base map code 64)?
  2. Which soil type has the largest relative overlay with forests compared with the expected overlay extent in case of spatial randomness?
  3. Which soil types are preferred for forested land according to statistical significance values?
  4. Add the tables you used in answering the questions.


  • Open the calculator of spatial data.
  • Select Categorical Overlay.
  • 200 is enough for random shifts. A larger number would result in a more reliable estimation of expected values and confidence intervals but increases the risk of System.Web.HttpException: Request timed out.
  • Select rst files mentioned in the exercise.
  • Press Calculate.
  • Wait while server responds the results. It should take up to 10 seconds.
  • It is more convenient to explore the results in Excel. There is a button near results for export.
  • The first table of results displays the number of pixels in category combinations.
  • The second table contains extent of overlay relative to the expected value in case of random relative location of categories.
  • The third table presents statistical significance as the probability of randomness of the relative overlay.
  • To answer the third question, you should compare those values in the third table, which corresponding values in the second table are >1. Significant preference is asked, not avoidance.
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