How to calculate the neighbouring grids on geohash. Algorithms required

Question

Hi I am working with a database with an implementation of geohash

So as shown above, as the zoom level goes down (6 zoom levels), more of abcd gets inserted into each grid. I have represented them as a rigid grid; however, the central point is different for all the grids. So for example, distance from a to b will not be the same as distance from a to c.

If it was a rigid grid, I can just get the closest four neighbouring grids; however, I cannot do that as the distances vary and the closest neighbours are not necessarily orthogonal. Only information that I have from the database is the centra point of each grid and the geohash key e.g. aa, ab, etc..

How will I find girds that are just north, west, east and south of each grid for every zoom level? (have 6 zoom levels)

Answer 1

As you can see a cell that ends in, for example, d, has a cell with the same prefix but ending in b north of it. This allows you to set up a mapping table.

In the cases where, like cb going north, you end up at ad, the trick is to recognize that going north from *b you need to look at the previous character (in this case, the c), go north from that character (a) and add the south-most edge of that column (d).

In short, it's a matter of implementing some mapping tables and some logic to deal with the edges.