Base layers

Principle

It is often useful to separate base layers as a reference and thematic layers in a Web map. In Lizmap, you can use groups or layers as base layers. It is also possible to use external services in the Web map.

The base layers are not part of the legend and are presented as a list.

Note

If a single base layer is configured (project layer, external service or empty base layer), then Lizmap Web Client interface does not show the box Base layers, but the layer will be however visible below the other layers.

Configuring the tool

The Base layers tab lets you add external services as base layer and an empty base layer. The empty base layer will display thematic layers over the project background color.

The available base layers

• OpenStreetMap, mapping project under free and open licenses:

  • OSM Mapnik: service available on openstreetmap.org

• ThunderForest, company using OSM data and providing tiles: * Open Cycle Map: OpenStreetMap cycling data including altitude information

• Google, requires compliance to use licence agreement:

  • Streets: the default Google Maps background layer

  • Satellite: the background map incorporating aerial and satellite images

  • Hybrid: the background map mixing streets and satellite

  • Terrain

• Bing Map, requires compliance with the Microsoft license agreement and therefore a key:

  • Streets: the default Bing Map background layer

  • Satellite: the background map incorporating aerial and satellite images

  • Hybrid: the background map mixing streets and satellite

• IGN Géoportail, requires compliance with the IGN license agreement and therefore a key:

  • Plan: The IGN rendering for the Web

  • Satellite: the background map incorporating IGN aerial and satellite images

  • Scan: the background map mixing the various IGN scan

  • Cadastre

The licenses are available at the following URLs:

• OpenStreetMap: https://wiki.openstreetmap.org/wiki/Tile_usage_policy

• Google: https://cloud.google.com/maps-platform/terms/

• Bing: https://www.microsoft.com/en-us/maps/product

• IGN: https://depot.ign.fr/geoportail/api/develop/tech-docs-js/fr/license.html

Scale with external base layer

All these external base layer are provided only in EPSG:3857 / Pseudo Mercator from the provider. The scale of such layer are fixed by the projection EPSG:3857.

Warning

As a result, if you choose an external base layer, the project will be displayed in Google Mercator EPSG:3857. Therefore, if you have specified multiple scales in the Lizmap configuration, these intermediate scales won’t be used. Only the minimum and maximum scale are used in this case. Read below about approximate scales.

QGIS Server will perform on the fly reprojection for your data. It is therefore necessary to prepare the QGIS project accordingly.

The Google Mercator coordinate reference system must be added in the Web Services CRSs list with the Project properties ‣ QGIS Server ‣ WMS.

This is a list of a very approximate integer scale for a given zoom level for the EPSG:3857:

0   500 000 000
1   250 000 000
2   150 000 000
3   70 000 000
4   35 000 000
5   15 000 000
6   10 000 000
7   4 000 000
8   2 000 000
9   1 000 000
10  500 000
11  250 000
12  150 000
13  70 000
14  35 000
15  15 000
16  8 000
17  4 000
18  2 000
19  1 000
20  500

Warning

These scales are just a hint of the scale. It is not possible to have rounded scale like this with EPSG:3857.

Visit the OpenStreetMap website at the country level and check how the scale is changing while panning/zooming.

https://www.openstreetmap.org/#map=6/48.995/4.856

External Lizmap layers

This feature has been removed. It’s replaced by the possibility of using the menu Layer ‣ Embed Layers and Groups, and in the plugin Layers tab declare the parent project and the Lizmap repository for the embed layers and groups. See Centralizing the cache with the integration of groups and layers from a master project