Misleading area calculations using occurrence data (AOOarea function)

[gepinillab]

Hi again,

When calculating the AOO based on the occurrence of a particular feature, it is important to consider that if multiple occurrences of that feature are present in the same pixel, the area calculation will be skewed.

To illustrate this point, I have created an example using occurrence data in Manhattan. Using a dataset of 1000 random points within Manhattan, I attempted to estimate the area of Manhattan using these points. However, because several points are in the same pixels, the resulting area estimation was over 4000 km², which is clearly an inaccurate and misleading result. Manhattan's actual area is only 60 km².

I have included the code for the example in Manhattan below:

library(tigris)
library(terra)
library(changeRangeR)
library(raster)

# Get Manhattan polygon
mh <- tigris::tracts(state = '36', county = '061')
mh <- tigris::erase_water(mh)
sf::sf_use_s2(FALSE)
mh <- sf::st_union(mh) %>% sf::st_buffer(dist = 0)
plot(mh)
## Area
terra::expanse(terra::vect(mh), unit = "km")
### 59.1 km2 (match Wikipedia)

## To WGS 84
mh <- terra::project(terra::vect(mh), y = "EPSG:4326") %>% 
  sf::st_as_sf()
# Create 1000 points inside Manhattan
pts <- terra::spatSample(terra::vect(mh), 1000, method = "regular") %>% 
  sf::st_as_sf()
# AOO based on points ###
## cRR
### Points need to be in WGS84 and it requires a template raster
r <- rast(mh, res = 1/120)
values(r) <- 1
rWGS84 <- terra::mask(r, mh)
### Run
crrPts <- changeRangeR::AOOarea(methods::as(r, "Raster"), 
                                sf::st_coordinates(pts))
print(crrPts$area) # Bug: 4072 km2!!!

Let me know if you have any questions.