![]() For example, if you had a GeoJSON property called categories and it was an array: "categories": Tools like Mapnik will turn arrays and objects into strings, which requires the decoder to parse them. The specification doesn't cover how to encode these values and is up to the encoder to decide. How to encode attributes that aren't strings or numbersĪttributes in geometric data, such as the properties object in GeoJSON can include more than strings and numbers. Consider this specification like how the PNG spec explains how to pack data. This specification does not cover how to store, request, or share vector tiles. This is something that has been considered for the future, but it will likely be a separate specification. ![]() This specification IS NOT intended to explain how to use vector tiles as a dataset. But, there are some related concepts that this specification does not cover. This specification is explicit in the way a vector tile should pack data. Visit Mapbox Vector Tiles for a list of tools implementing vector tiles. Servers: support rendering and serving up vector tiles ( note: the specification doesn't go into how to do this explicitly).Applications: browser-based tools for creating and visualizing vector tiles.Clients: web-based tools that render vector tiles that conform to the specification.Parsers & generators: libraries that read and/or encode vector tiles, some also have command line utilities.Many of them fall into one of the following categories: Implementations of the Mapbox Vector Tile Specification are far and wide. Note: the Y axis is positive-downward in vector tile coordinates! Each example assumes all rings are part of the same multipolygon. The following example geometries show how encoding a ring's winding order can affect the rendered result. Exterior rings must be oriented clockwise and interior rings must be oriented counter-clockwise (when viewed in screen coordinates). Any polygon interior ring must be oriented with the winding order opposite that of their parent exterior ring and all interior rings must directly follow the exterior ring to which they belong. Yet, with the introduction of client side rendering of vector tiles via GL technologies, the raw geometry data has become useful for a source of information outside of rendering.įor renderers to appropriately distinguish which polygons are holes and which are unique geometries, the specification requires all polygons to be valid ( OGC validity). It is important to be able to infer winding order to extract source data from a vector tile and understand if the geometry is part of a multipolygon or a unique polygon.Įxtracting the original data from images has been difficult on maps in the past, because of the loss of underlying metadata from the geometry that might have been used to create the image. Many geometries are multipolygons with "holes," which are also represented as polygon rings. Winding order refers to the direction the vector tile draws a ring, either clockwise or counter-clockwise. It follows the commands of the "pen" to encode two rings. This is a step-by-step example showing how a single vector tile encodes geometry in the grid. They encode points, lines, and polygons as x/ y pairs relative to the top left of the grid in a right-down manner. Vector tiles hold no concept of geographic information. ![]() To encode geographic information into a vector tile a tool must convert geographic coordinates, such as latitude and longitude, into vector tile grid coordinates. Mapbox Vector Tiles and OpenStreetMap PBFs are protobuf files, but conform to completely different specifications and are used in different ways. PBFs are a format, much like XML and can take many forms. Mapbox Vector Tiles are not related at all to OpenStreetMap PBF files. The specification details are largely structured around the rules implemented in the base. For clarity, Mapbox Vector Tiles use the. Vector tiles are encoded as Google Protobufs (PBF), which allow for serializing structured data. This guide covers file format, examples of geometry encoding and attribute encoding, an explanation of the importance of winding order, and a list of concepts not included in the Mapbox vector tile specification.įor information about file formats and extensions, projections and bounds, and the internal structure of vector tiles, you can read the Mapbox Vector Tile Specification on GitHub. Understanding these standards can help you understand how to work with Mapbox vector tiles. Just as applications make assumptions about what information exists in a database, so do Mapbox tools make assumptions about how vector tiles store geographic information. This guide on vector tile standards explains how data is stored and encoded in vector tiles. ![]()
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