Tile Map Service (TMS)

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Introduction

Tile Map Service (TMS) is a network-based geographic information service protocol for efficiently loading and displaying map data. The core idea of TMS is to pre-cut map data into small tiles of fixed size (usually 256×256 pixels), and store and access them in a hierarchical (zoom level) and spatial index manner. The client dynamically requests the corresponding tiles according to the user’s view requirements, thereby achieving fast loading and smooth display. TMS usually organizes map data in the form of tile pyramids, which are gradually refined from the global view (low zoom level) to the local details (high zoom level), and the resolution of each level increases, so as to meet the multi-scale display requirements.

Data Format Overview

The core data formats used by TMS mainly include:

1. Image format

Common formats: JPEG, PNG, WEBP, etc.
Usage: JPEG is usually used for natural objects (such as satellite images) because of its high compression rate and good visual effects; PNG and WEBP are more suitable for vector maps or layers that require transparent backgrounds.

2. Metadata file

Describes the metadata of the slice hierarchy, coordinate system, projection method, etc. Common metadata formats are XML and JSON.

3. Coordinate system and projection method

Coordinate system: Usually Web Mercator (EPSG:3857) to achieve compatibility with most online map services (such as Google Maps, Bing Maps).
Projection method: Using Mercator Projection, it can provide sufficient accuracy and performance in most application scenarios.

4. Tile index system

TMS slices use a three-dimensional index system of Z (zoom level), X (horizontal axis index), and Y (vertical axis index) to locate and store each tile.

Pros

1. Efficient loading: By loading in blocks, only tiles within the current view range are requested, which greatly reduces the amount of data loaded and improves the loading speed.

2. Strong compatibility: TMS is an open protocol that is compatible with a variety of GIS platforms and online map services, such as Leaflet, OpenLayers, and Mapbox.

**3. Support for multi-level zooming: **The tile pyramid structure supports multi-level display from global to local, meeting the user’s multi-level view requirements.

4. Easy to cache: Due to the fixed size and unique index of each tile, the TMS service is very suitable for static file caching, and CDN and other technologies can be used to further optimize loading performance.

Cons

1. Large storage space: Since tiles of all zoom levels need to be generated in advance, especially at high resolution, the amount of data will expand dramatically, occupying a large amount of storage space.

**2. Poor dynamicity: **Tiles are usually not easy to modify after generation. TMS is not suitable for dynamic data scenarios that need to be updated frequently (such as real-time traffic information).

3. High initial generation cost: Making tile pyramids requires preprocessing a large amount of data, which takes a long time to generate and requires additional configuration tools and servers.

Application Scenario

Tile Map Service is widely used in various scenarios that require fast loading and visualization of geographic data. For example, in services such as Google Maps and Bing Maps, they are used to achieve a smooth map browsing experience. In Web GIS systems, TMS data is loaded through libraries such as Leaflet and OpenLayers to provide users with interactive map displays. Governments and enterprises use TMS to display infrastructure, land use, etc. to support decision analysis and public services. Through TMS, research institutions and enterprises can quickly share large-scale remote sensing images and terrain data. The multi-level and block loading mechanism of TMS is also suitable for terrain rendering in large virtual scenes and map games.