Bigger buffer needed for static feature processing around London boundary

[PatrickOHara]

Describe the bug

Hex grids on the edge of London boundary are not calculating the static features correctly. Notice in the figure below how the grid cells on the boundary are blue, representing that there is "less road" in the buffer zone.

The buffer zone extends beyond the London boundary, particularly when the buffer zone is 1000m. But because we prune all roads outside of the London boundary in a pre-processing step, these total road is small.

Expected behavior

The way we pre-process is to intersect each static dataset (road network, UK Map,) with the London boundary.

What we expect is each static dataset should be intersected with the London boundary plus 1000 meters buffer around the edge of the boundary.

This should mean any static feature extraction algorithm does not "run out of features" near the edge of the boundary.