Make edge list an edge map

[hellkite500]

The *_edge_list.json files generated are lists of edge mappings:

[
  {
    "id": "cat-27",
    "toid": "nex-26"
  },
  {
    "id": "cat-52",
    "toid": "nex-34"
  },
  {
    "id": "cat-67",
    "toid": "nex-68"
  }
]

This is really just a map, and would likely be better suited for look ups if structured as one:

{
    "cat-27": "nex-26",
    "cat-52": "nex-34",
    "cat-67": "nex-68"
}

[dblodgett-usgs]

What's the argument for the change? It's more compact, but losing the "id" "toid" makes the data a little too cryptic for my taste.

[hellkite500]

The argument is very similar to the crosswalk change already implemented. Keeping a list of objects requires iteration of the list to find a s single element, whereas bringing the local id out and mapping from that allows quick lookup of elements by id.

It could look more like the crosswalk and still not require iterating:

{
    "cat-27": {
        "toid": "nex-26"
    },
    "cat-52": {
        "toid": "nex-34"
    },
    "cat-67": {
        "toid": "nex-68"
    }
}

[dblodgett-usgs]

OK -- we can do this. I wonder if there's a better form for topology though? Is this a pressing need or can I back burner?

[hellkite500]

Obviously pressing, can't you tell?

[dblodgett-usgs]

catchment_edge_map.json
{
  "cat-8895442": "nex-250031932",
  "cat-8895520": "nex-250031930",
  "cat-8895396": "nex-250031903",
  "cat-8895402": "nex-250031930",
  "nex-250031932": "cat-8895402",
  "nex-250031930": "cat-8895396",
  "nex-250031903": "cat-0"
}

or:

catchment_edge_map.json
{
  "cat-8895442": {
    "toid": "nex-250031932"
  },
  "cat-8895520": {
    "toid": "nex-250031930"
  },
  "cat-8895396": {
    "toid": "nex-250031903"
  },
  "cat-8895402": {
    "toid": "nex-250031930"
  },
  "nex-250031932": {
    "toid": "cat-8895402"
  },
  "nex-250031930": {
    "toid": "cat-8895396"
  },
  "nex-250031903": {
    "toid": "cat-0"
  }
}

[hellkite500]

I would go with the first form:

catchment_edge_map.json
{
  "cat-8895442": "nex-250031932",
  "cat-8895520": "nex-250031930",
  "cat-8895396": "nex-250031903",
  "cat-8895402": "nex-250031930",
  "nex-250031932": "cat-8895402",
  "nex-250031930": "cat-8895396",
  "nex-250031903": "cat-0"
}

To enforce a 1-1 mapping.