Computes three different summary statistics: (1) TotalArea total area of each polygon; (2) AreaCovered area covered by a multipolygon object within a high order polygon; and, (3) Ratio ratio between AreaCovered and TotalArea i.e. ratio between an area covered by a given set of features and total area of a higher-order geography polygon.

areal_calc(polygon_layer, higher_geo_lay, unique_id_code, crs)

## Arguments

polygon_layer multipolygon object of class sf, sfc or sfg. multipolygon object of class sf, sfc or sfg. a string; indicating a unique ID column of higher_geo_lay, used as the summary areas. coordinate reference system: integer with the EPSG code, or character based on proj4string.

## Value

a tibble data frame object containing four columns is returned:

• the unique_id_code of higher_geo_lay

• the total area of each polygon in higher_geo_lay (TotalArea),

• the total area covered by polygon_layer features (AreaCovered),

• the ratio between the total area covered by polygon_layer and total area of higher_geo_lay polygon (Ratio).

## Details

The function requires two sets of polygon data: high-order and low-order geographic polygons

## Examples

## Run areal_calc() using the packages' dummy data sets.
## The data sets are georeferenced on wgs84. However, a planar system is used to measure areas.
## For the examples provided here, points and polygons relate to the United Kingdom.
## So the British National Grid is used.

## Not run:
#outcome <- areal_calc(polygon_layer = pol_small,
#higher_geo_lay = pol_large,
#unique_id_code = "large_pol_",
#crs = "epsg:27700")
## End(Not run)