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# Data Types

The impact functions essentially combine spatial data in different formats through a common interpolation library. This essentially allows values from one data set to be assigned to another independent of their types. Given two layers H and E, say, the call:

    I = assign_hazard_values_to_exposure_data(H, E, ...)

will produce a new layer with all values from H transferred to E in a manner appropriate for the data types of H and E. Generally, existing values in E will be also be carried over to I. Conceptually, the new layer I represents the values of H interpolated to E.

The function takes a number of optional keyword arguments that pertain to certain type combinations. They are

- layer_name: Optional name of returned layer. If None (default) the name of the exposure layer is used.
- attribute_name:
  - If hazard layer is of type raster, this is the name for new attribute in the result containing the hazard level. If None (default) the name of hazard is used
  - If hazard layer is of type vector, it is the name of the attribute to transfer from the hazard layer into the result. If None (default) all attributes are transferred.
- mode: Interpolation mode for raster to point interpolation only. Options are ‘linear’ (default) or ‘constant’

The following table shows allowed combinations and what interpolation means in each case.

H | E | Methodology | Return value
--- | --- | --- | ---
Polygon | Point | Clip points to polygon and assign all attributes | Point
Polygon | Line |  | N/A
Polygon | Polygon |  | N/A
Polygon | Raster | Convert to points and use Polygon-Point algorithm | Point
Raster | Point | Bilinear or piecewise constant interpolation | Point
Raster | Line |  | N/A
Raster | Polygon | Convert to centroids and use Raster-Point algorithm | Polygon
Raster | Raster | Check that rasters are aligned and return E | Raster

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