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Exercise 3941. Points 3, theme: Trend Surface

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  1. Create a linear model describing the spatial trend in the annual mean precipitation given in the attached data. Write the model formula as the first item in your answer.
  2. Is the precipitation amount higher in the east or in the west, in the north or in the south?
  3. How much of the variability in these precipitation data is described by this model?
Data: SADEMED.xls


  • A linear trend surface is defined by a regression model where the spatial coordinates are the explanatory variables. It means tools designed for classical non-spatial statistics can be used for creating a spatial trend. For example, the spatial data calculator includes a page for linear regression.
  • The exercise can be solved either using WGS coordinates or Cartesian coordinates. The answer in database is calculated using Cartesian coordinates.
  • Check which coordinate is the first in the given table of Cartesian coordinates — north direction or east direction. North direction is distance from the equator in meters. Is The distance from Estonia to the equator about 600 or 6000 km?
  • In addition, the decimal separator can be either point or comma and the empty lines are automatically excluded. Thanks to this, whole columns can be copied from Excel, not just blocks of cells.
  • The proportion of variability described by a model is measured by the R² statistic.
  • Do not forget to add the meaning of abbreviations used in the model formula.
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