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Distribution of sampling efforts

Sampling in quadrates, polygones or transects
Three different strategies for sampling in a coastal area: quadrates (q), transects (t) and polygons (p). Each strategy covers the same total area but differs in distribution. Grid cells represent the spatial resolution of subsequent model.

Point sampling has many advantages
For many biological features there are three basic approaches to sampling; points (quadrates), transects and polygons. Quadrate sampling has many advantages from a modelling point of view, if conducted in an appropriate way with respect to necessary taxonomic detail, modelling resolution, precision and representativity:

  • resolution of sampling corresponds to that of the model grid size
  • sampling units and effort is distributed in a representative way
  • the number of independent samples is maximised

Existing data may be transformed

Sometimes modelling has to be based on existing data collected from transects or polygons. If so, the sampling units (transects and polygons) need to be split up in units which correspond to the desired resolution. Here, it is very important to minimise and evaluate bias caused by lack of independence (”spatial autocorrelation”) and lack of representativity. To some degree this can be done by selecting appropriate modelling techniques but one option may be to sacrifice data to ensure independence (see Nyström Sandman, 2011).

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