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Re: AI-GEOSTATS: forests on slopes

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  • Patrick van Laake
    ... Chuck, I completely agree with you. Too many people already use data that is not suitable for the kind of analysis they are trying to perform, either
    Message 1 of 4 , Dec 5, 2000
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      Chuck Ehlschlaeger wrote:

      > >> "How much of the world's forests are located on slopes greater than 10%?"
      > >
      > >
      > >> Ideally, an answer would consist of a frequency distribution of forests by slope class.
      > >>
      > >
      > > I suggest you browse to the website of the EROS Data Center of the USGS. There you can pick up GTOPO30, a 30 arc-second DEM from which you can extract slope. While you are there, you can pick up the SLCR (for
      > > Seasonal Land Cover Region) data set which indicates different forest types a.o. land use classes. Both data sets are global and have a cell size of about 1km.
      > >
      > > With this data (and the right GIS software) you can yourself derive statistics for any slope class, slice, correlate with other data sets, differentiate by continent, ecoregion, forest type, and many more things.
      > >
      >
      > Before you spend time downloading files, you should ask yourself the
      > following questions:
      >
      > 1) What is MY definition of slope?
      >
      >
      > 2) What is MY definition of forest?
      >
      >
      > In summary, find or build the data that will answer the question. Don't
      > use whatever data is available.
      >

      Chuck, I completely agree with you. Too many people already use data that is not suitable for the kind of analysis they are trying to perform, either because there is no better data, but more likely so because they do
      not know how to evaluate improperly documented data and therefore know no better.

      Remco's question, however, explicitly stated global coverage. Apart from the computational limitations in choosing a finer granularity of the data, there are two reasons why I so casually mentioned these two data
      sets:

      * They are the best data sets available with "uniform" global characteristics (GTOPO30 is actually constructed from many different sources with varying degrees of fidelity). For instance, both data sets are being used
      by the Food and Agriculture Organization of the UN to construct their Forest Resources Assessment 2000 analysis, if that is any indication.

      * At a global scale the problem generalization and data aggregation that are generally applied do not merit or even support using better data. Remco's request for a frequency distribution to me seems coincident with
      this.

      Still, the call on using this data is Remco's.

      Regards,
      Patrick


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