MultiPolygon Support

[jguthmiller]

If more than one polygon exists for a unique feature in a given tile, the parseVectorTileLayer method will end up overwriting the existing references to that feature, and add a copy of itself to the features list for that tile.

For example, the islands off the coast of California should be visible; Instead the last California
polygon in the list of polygons for that tile was effectively duplicated.

Here's the decoded json of the tile for reference. I used Tilestache to generate the tiles, and Mapzen's mapbox vector tile library to encode them.

{
  "states": [
    {
      "geometry": [
        [
          4096,
          2231
        ],
        [
          3532,
          2232
        ],
        [
          3534,
          4096
        ],
        [
          4096,
          4096
        ],
        [
          4096,
          2231
        ]
      ],
      "properties": {
        "label": "Utah"
      },
      "id": 24
    },
    {
      "geometry": [
        [
          3898,
          0
        ],
        [
          3252,
          240
        ],
        [
          3294,
          342
        ],
        [
          3355,
          346
        ],
        [
          3379,
          386
        ],
        [
          3362,
          464
        ],
        [
          3308,
          467
        ],
        [
          3292,
          491
        ],
        [
          3305,
          565
        ],
        [
          3283,
          584
        ],
        [
          3285,
          629
        ],
        [
          3358,
          693
        ],
        [
          3354,
          861
        ],
        [
          3396,
          931
        ],
        [
          3502,
          1005
        ],
        [
          3485,
          1043
        ],
        [
          3409,
          1091
        ],
        [
          3378,
          1203
        ],
        [
          3318,
          1275
        ],
        [
          3314,
          1376
        ],
        [
          3342,
          1413
        ],
        [
          3302,
          1554
        ],
        [
          3290,
          1691
        ],
        [
          3308,
          1720
        ],
        [
          3274,
          1818
        ],
        [
          3319,
          1843
        ],
        [
          3406,
          1842
        ],
        [
          3457,
          1787
        ],
        [
          3494,
          1790
        ],
        [
          3533,
          1866
        ],
        [
          3532,
          2232
        ],
        [
          4096,
          2231
        ],
        [
          4096,
          0
        ],
        [
          3898,
          0
        ]
      ],
      "properties": {
        "label": "Arizona"
      },
      "id": 1
    },
    {
      "geometry": [
        [
          3532,
          2232
        ],
        [
          3533,
          1866
        ],
        [
          3494,
          1790
        ],
        [
          3457,
          1787
        ],
        [
          3406,
          1842
        ],
        [
          3319,
          1843
        ],
        [
          3274,
          1818
        ],
        [
          3308,
          1720
        ],
        [
          3290,
          1691
        ],
        [
          3302,
          1554
        ],
        [
          3342,
          1413
        ],
        [
          3314,
          1376
        ],
        [
          3322,
          1332
        ],
        [
          2275,
          2332
        ],
        [
          1364,
          3155
        ],
        [
          1365,
          4096
        ],
        [
          3534,
          4096
        ],
        [
          3532,
          2232
        ]
      ],
      "properties": {
        "label": "Nevada"
      },
      "id": 19
    },
    {
      "geometry": [
        [
          1231,
          923
        ],
        [
          1253,
          899
        ],
        [
          1201,
          904
        ],
        [
          1231,
          923
        ]
      ],
      "properties": {
        "label": "California"
      },
      "id": 35
    },
    {
      "geometry": [
        [
          1964,
          375
        ],
        [
          1909,
          389
        ],
        [
          1871,
          467
        ],
        [
          1964,
          375
        ]
      ],
      "properties": {
        "label": "California"
      },
      "id": 35
    },
    {
      "geometry": [
        [
          1519,
          574
        ],
        [
          1571,
          551
        ],
        [
          1530,
          554
        ],
        [
          1519,
          574
        ]
      ],
      "properties": {
        "label": "California"
      },
      "id": 35
    },
    {
      "geometry": [
        [
          1958,
          631
        ],
        [
          1982,
          588
        ],
        [
          1924,
          595
        ],
        [
          1915,
          635
        ],
        [
          1873,
          661
        ],
        [
          1958,
          631
        ]
      ],
      "properties": {
        "label": "California"
      },
      "id": 35
    },
    {
      "geometry": [
        [
          1376,
          864
        ],
        [
          1323,
          843
        ],
        [
          1274,
          890
        ],
        [
          1349,
          905
        ],
        [
          1376,
          864
        ]
      ],
      "properties": {
        "label": "California"
      },
      "id": 35
    },
    {
      "geometry": [
        [
          1390,
          916
        ],
        [
          1497,
          895
        ],
        [
          1539,
          904
        ],
        [
          1431,
          872
        ],
        [
          1390,
          916
        ]
      ],
      "properties": {
        "label": "California"
      },
      "id": 35
    },
    {
      "geometry": [
        [
          1364,
          3155
        ],
        [
          2275,
          2332
        ],
        [
          3322,
          1332
        ],
        [
          3318,
          1275
        ],
        [
          3378,
          1203
        ],
        [
          3409,
          1091
        ],
        [
          3485,
          1043
        ],
        [
          3502,
          1005
        ],
        [
          3396,
          931
        ],
        [
          3354,
          861
        ],
        [
          3358,
          693
        ],
        [
          3285,
          629
        ],
        [
          3305,
          565
        ],
        [
          3292,
          491
        ],
        [
          3379,
          441
        ],
        [
          3355,
          346
        ],
        [
          2412,
          251
        ],
        [
          2396,
          311
        ],
        [
          2368,
          309
        ],
        [
          2338,
          506
        ],
        [
          2286,
          582
        ],
        [
          2045,
          781
        ],
        [
          1995,
          760
        ],
        [
          1943,
          776
        ],
        [
          1951,
          819
        ],
        [
          1904,
          901
        ],
        [
          1799,
          889
        ],
        [
          1682,
          934
        ],
        [
          1627,
          1007
        ],
        [
          1524,
          1072
        ],
        [
          1409,
          1069
        ],
        [
          1313,
          1098
        ],
        [
          1200,
          1084
        ],
        [
          1133,
          1137
        ],
        [
          1130,
          1393
        ],
        [
          1053,
          1423
        ],
        [
          1043,
          1523
        ],
        [
          896,
          1628
        ],
        [
          818,
          1779
        ],
        [
          672,
          1917
        ],
        [
          644,
          2041
        ],
        [
          704,
          2087
        ],
        [
          714,
          2142
        ],
        [
          687,
          2200
        ],
        [
          662,
          2221
        ],
        [
          587,
          2217
        ],
        [
          489,
          2321
        ],
        [
          491,
          2395
        ],
        [
          447,
          2477
        ],
        [
          447,
          2597
        ],
        [
          325,
          2698
        ],
        [
          264,
          2688
        ],
        [
          291,
          2762
        ],
        [
          281,
          2814
        ],
        [
          8,
          3118
        ],
        [
          0,
          4096
        ],
        [
          1365,
          4096
        ],
        [
          1364,
          3155
        ]
      ],
      "properties": {
        "label": "California"
      },
      "id": 35
    }
  ]
}

[hallahan]

Ah, yes. Our ID dictionary should then refer to an array of features rather than just one.

I wonder if the Mapbox folks have any insight on how multi-polygons should be thought about in regards to the vector tile spec.

[adrpar]

+1 on seeing this fixed. Took me ages to realize what was going on when using the gs-mvt plugin for geoserver and trying to see if it is actually doing its job right...

[jguthmiller]

I hacked together a fix a while back, but wasn't sure about submitting a PR since version 2 of the vector tile spec addresses multipolygons.

Here's a copy of the patch if anyone's interested.

[guibsou]

hi @jguthmiller !
the patch is perfect.
thanks !