Vector Tile Cache

Vector tiles are a highly efficient format for web mapping. The core concept is to divide a project's vector data into tiles, similarly to raster tile systems (e.g., WMTS).

There are several standards for producing vector tiles. Mapbox introduced a format based on Google’s Protocol Buffers encoding ( https://developers.google.com/protocol-buffers). Known as MVT (Mapbox Vector Tiles), this format is widely supported by mapping tools including JMap Cloud, JMap Server, and JMap NG.

A tiling grid is applied to vector data, dividing it into tiles. Each tile can include features from multiple layers. A full set of tiles is generated for each zoom level. In web mapping, there are typically 23 levels:

• Level 0 represents the entire Earth

• Level 22 corresponds to street-level detail

Lower zoom levels use simplified geometry to reduce file size and improve performance.

Vector features (lines, polygons) are clipped at tile boundaries. When a geometry spans multiple tiles, it is split, and each tile stores only its part. The mapping application is responsible for reconstructing the complete geometry.

Feature attributes are embedded in the tiles, allowing dynamic and interactive data usage—for example:

• generating thematic maps on-the-fly

• applying attribute-based filters

Styles are not included within the tiles. Instead, they are defined in a separate JSON file. This allows applications to dynamically style data, eliminating the need to regenerate tiles when styles change.

Vector tiles can be generated on-the-fly or pre-generated and cached, significantly improving server response times and ensuring smooth user experiences.

Vector Tile Generation in JMap Cloud

A JMap Cloud project produces three types of data consumed by client applications:

1. Style JSON File This file accompanies the vector tiles and contains layer definitions, styles, thematics, etc.

2. Vector Tile Set (MVT) These tiles contain the geometry and attributes of non-editable layers. They can be generated:

   • on demand, as users navigate in JMap NG

   • ahead of time, then cached

3. GeoJSON Vector Data These represent the editable layers and are delivered on demand, by region.

Performance Factors for Vector Tiles

While vector tiles are generally lighter than raster tiles, several factors can affect tile size and impact JMap NG application performance:

• Number of attributes per layer More attributes increase tile size and load times.

• Layer visibility scales For dense layers, it is recommended to limit their visibility to higher zoom levels. This reduces data volume in low zoom tiles and accelerates tile generation.

• Caching Pre-generating and caching tiles greatly enhances performance.

Managing a Project’s MVT Cache

To manage a project’s vector tile (MVT) cache:

1. Click , then select MVT Cache to open the management interface. This interface includes four sections.

   Cache state	Indicates the cache status, if available.
   Fill	This option allows you to indicate whether you want to create tiles for all 23 levels or for a specific range of levels. In this case, specify the minimum and maximum levels of the range. This option does not overwrite tiles that are already cached.
   Delete	This option allows you to specify whether you want to remove tiles from all 23 levels or from a specific range of levels. In this case, indicate the minimum and maximum levels of the range.
   Running task	Indicates the progress of the creation or deletion by cache level as well as the overall progress of the creation or deletion.

2. Choose the task you want to perform.

3. Click Launch task. The Running task section shows progress visually and as a percentage.

4. To cancel a running task, click . A confirmation message will appear.