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Document tilestats
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e-n-f committed Nov 20, 2017
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154 changes: 148 additions & 6 deletions 1.3/spec.md
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Expand Up @@ -135,7 +135,11 @@ As mentioned above, Mapbox Vector Tile tilesets must include a `json` row in the
to summarize what layers are available in the tiles and what attributes are available for the
features in those layers.

The row contains the string representation of a JSON object with a `vector_layers` key, whose value is an array of layers.
### Vector_layers

The `json` row contains the string representation of a JSON object.

The object must contain a `vector_layers` key, whose value is an array of layers.
Each layer is a JSON object with the following keys:

* `id`: The layer ID, which is referred to as the `name` of the layer in the [Mapbox Vector Tile spec](https://github.com/mapbox/vector-tile-spec/tree/master/2.1#41-layers).
Expand All @@ -157,6 +161,14 @@ These keys are used to describe the situation where different sets of vector lay
appear in different zoom levels of the same tileset, for example in a case where
a "minor roads" layer is only present at high zoom levels.

### Tilestats

The `json` row may also contain a `tilestats` key, whose value is an object in the "geostats"
format documented in the [mapbox-geostats](https://github.com/mapbox/mapbox-geostats#output-the-stats)
repository. Like the `vector_layers`, it lists the tileset's layers and the attributes found
within each layer, but also gives sample values for each attribute and the range of values for
numeric attributes.

### Example

A vector tileset that contains United States counties and primary roads from [TIGER](https://www.census.gov/geo/maps-data/data/tiger-line.html) might
Expand Down Expand Up @@ -184,12 +196,9 @@ have the following metadata table:
"fields": {
"ALAND": "Number",
"AWATER": "Number",
"COUNTYFP": "String",
"GEOID": "String",
"MTFCC": "String",
"NAME": "String",
"NAMELSAD": "String",
"STATEFP": "String"
"NAME": "String"
}
},
{
Expand All @@ -204,6 +213,139 @@ have the following metadata table:
"RTTYP": "String"
}
}
]
],
"tilestats": {
"layerCount": 2,
"layers": [
{
"layer": "tl_2016_us_county",
"count": 3233,
"geometry": "Polygon",
"attributeCount": 5,
"attributes": [
{
"attribute": "ALAND",
"count": 6,
"type": "number",
"values": [
1000508839,
1001065264,
1001787870,
1002071716,
1002509543,
1003451714
],
"min": 82093,
"max": 376825063576
},
{
"attribute": "AWATER",
"count": 6,
"type": "number",
"values": [
0,
100091246,
10017651,
100334057,
10040117,
1004128585
],
"min": 0,
"max": 25190628850
},
{
"attribute": "GEOID",
"count": 6,
"type": "string",
"values": [
"01001",
"01003",
"01005",
"01007",
"01009",
"01011"
]
},
{
"attribute": "MTFCC",
"count": 1,
"type": "string",
"values": [
"G4020"
]
},
{
"attribute": "NAME",
"count": 6,
"type": "string",
"values": [
"Abbeville",
"Acadia",
"Accomack",
"Ada",
"Adair",
"Adams"
]
}
]
},
{
"layer": "tl_2016_us_primaryroads",
"count": 12509,
"geometry": "LineString",
"attributeCount": 4,
"attributes": [
{
"attribute": "FULLNAME",
"count": 6,
"type": "string",
"values": [
"1- 80",
"10",
"10-Hov Fwy",
"12th St",
"14 Th St",
"17th St NE"
]
},
{
"attribute": "LINEARID",
"count": 6,
"type": "string",
"values": [
"1101000363000",
"1101000363004",
"1101019172643",
"1101019172644",
"1101019172674",
"1101019172675"
]
},
{
"attribute": "MTFCC",
"count": 1,
"type": "string",
"values": [
"S1100"
]
},
{
"attribute": "RTTYP",
"count": 6,
"type": "string",
"values": [
"C",
"I",
"M",
"O",
"S",
"U"
]
}
]
}
]
}
}
```

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