Functionality for adjacent tiles / quadkeys

[daniel-j-h]

There is a parent and a children function to go up or down the tile hierarchy, respectively.

But there is no function right now to go "sideways" to get a tile's siblings on the same zoom level.

Use cases are e.g. buffering a tile with its eight adjacent tiles. I'm finding myself writing small utility functions for this every now and then again and can imagine other people do, too. It would be great to have it in mercantile 🤗

What do you think the api should look like? Something as simple as

mercantile.adjacent_tile(tile)

or more advanced e.g. with a generator returning neighboring tiles and the level they are on (as in breadth-first-search)?

The latter would allow users to re-use this function when they not only want to get one level of adjacent tiles. 🌐

Thoughts? 🤔

[sgillies]

@daniel-j-h I agree, adjacent tiles would be a nice addition to the API, even without being very advanced. Let's say you have an irregular blob of tiles: a combination of adjacent_tiles() and Python's set could let you build up an irregular buffer quite nicely.

Can you say more about generalizing to the Z dimension? Would the parent's neighbors be included? Would the neighbors of every child be included?

[daniel-j-h]

Exactly! Adjacent tiles and set is what I'm using to buffer tiles and then do de-duplication! 🌐

I think I was not clear about the generalization. I don't want to generalize adjacent tiles for different zoom levels.

What I was suggestion instead was generalizing on how many levels of adjacency we want to return.

See this beautifully manually drawn diagram depicting a tile x and its closest friends 👨‍👧‍👦

o o o o o o o
o z z z z z o
o z y y y z o
o z y x y z o
o z y y y z o
o z z z z z o
o o o o o o o

My questions are

1. Should we provide a simple adjacent_tiles(x) returning [y, ...] (one level of adjacency)
2. Should we prodive a more advanced adjacent_tiles(x, 2) returning [(x, 0), (y, 1)..., (z, 2)...]
3. Should we provice 2 as a generator and provide two generators, one to walk in depth-first [(x,0), (y, 1), (z, 1), ...] and one in breadth first order [(x, 0), (y, 1), (y, 1), ...]?
4. Should x be included in the returned tiles (maybe not because neither parent not children does this)?

Happy Weekend folks ✌️

[dnomadb]

@daniel-j-h I was working on a command like this a while back: mapbox/supermercado#19

[daniel-j-h]

Coolio! 🙌 Should we consider this then as advanced functionality and it should go in the supermercado project? And only have the adjacent tile function here, returning directly neighboring tiles?