Vector Tile Structure

Vector Tiles are served in binary format, which uses Google Protocol Buffers as the method of serializing structured data. The serializing algorithm is very effective and as a result Vector Tiles are light-weight.

Vector Tile diagram

The following diagram shows dependencies between the properties of vector tile.

Legend

Tile

Represents a vector tile as a whole entity. It consists of at least one TileLayer.
If the tile does not contain any relevant data, it contains one layer named empty.

TileLayer

Part of a Tile, representing one of the layers that can be rendered later. In the Traffic API it can represent all of the traffic flow or all of the traffic incidents.
Every TileLayer contains the following fields:

• name
• version
• extent

It may also contain the following fields:

• keys are an array of unique strings.
• values are an array of unique TileValues.
• features are an array of unique TileFeatures.

Arrays of keys and values contain the mapping for tags of TileFeature.

TileFeature

Member of an array of features stored in a TileLayer, containing a geometry representation that can be rendered.
It always contains the following fields:

• type is a type of geometry. It can be point, linestring, or polygon.
• geometry is an array of encoded geometry that can be used for rendering. See the Decoding tile geometry section for details.

It may also contain the following fields:

• tags are an array containing properties of feature.
  • They are a TileFeature's detailed description which can be used for styling and later rendering the geometry.
  • They are encoded into an array of integers.
  • In order to decode them, the arrays of keys and values, from corresponding TileLayer must be used.
  • See the Decoding tile tags section for details.

TileValue

Encoded representation of a string, integer, floating point, or boolean value.

• It is stored in a values array, in a TileLayer.
• It is used for decoding tags of a TileFeature (together with the members of a keys array).
• See the Decoding tile tags section for details.

Formally, the structure of Vector Tile is described by the protocol buffer schema. It allows the generation of C++, Java, Python, Go, Ruby, Objective-C and C# code based on proto file.

package vector_tile;

option optimize_for = SPEED;

message Tile {

    enum GeomType {
        UNKNOWN = 0;
        POINT = 1;
        LINESTRING = 2;
        POLYGON = 3;
    }

    message Value {
        optional string string_value = 1;
        optional float float_value = 2;
        optional double double_value = 3;
        optional int64 int_value = 4;
        optional uint64 uint_value = 5;
        optional sint64 sint_value = 6;
        optional bool bool_value = 7;
        extensions 8 to max;
    }

    message Feature {
        optional uint64 id = 1 [ default = 0 ];
        repeated uint32 tags = 2 [ packed = true ];
        optional GeomType type = 3 [ default = UNKNOWN ];
        repeated uint32 geometry = 4 [ packed = true ];
        optional bytes raster = 5;
    }

    message Layer {
        required uint32 version = 15 [ default = 1 ];
        required string name = 1;
        repeated Feature features = 2;
        repeated string keys = 3;
        repeated Value values = 4;
        optional uint32 extent = 5 [ default = 4096 ];

        extensions 16 to max;
    }

    repeated Layer layers = 3;

    extensions 16 to 8191;
}