# Offline Use of Mergin Maps Mobile App

The Mergin Maps mobile app app can be used without internet connection, which is useful if you need to do the field survey in areas with poor cell phone signal or limited mobile internet. Collecting data in the field and synchronising them in the office using WiFi can be also more effective when working with large files.

However, there are some actions that require internet connection and cannot be done offline, such as synchronising changes to the cloud, displaying online background maps or working with online PostGIS layers. Also, if you are offline, you will not be able to switch accounts or download projects from the cloud.

# Offline field survey workflow

Here is a typical workflow of offline data collection.

We assume that the field surveyors have already installed the mobile app and are signed in, as well as that the project used for field survey follows recommendations described in How to set up an offline Mergin Maps project.

  1. Make sure that your Mergin Maps project is synchronised to the Mergin Maps cloud
  2. While being online, field surveyors download the project to their mobile device using Mergin Maps mobile app
  3. Now they can go to do the field survey and collect data and photos while being offline
  4. After finishing field survey and being back online in the office, all surveyors upload their changes back to the cloud

# How to set up an offline Mergin Maps project

Let's see what needs to be done when preparing the Mergin Maps project in QGIS so that all data are available locally in your mobile device and the internet connection is not needed during the field survey.

Whether creating a new Mergin Maps project or editing an existing one, you have to see which layers in your project require internet connection.

Layers that were packaged when creating a new Mergin Maps project in QGIS are stored in the cloud. When the project is downloaded to Mergin Maps mobile app, they are automatically downloaded to your mobile device and can be used offline in the same way as if you were online.

In general, layers that do not work offline are:

  • online background maps, such as WMS/WMTS, WFS or online XYZ tiles
  • online PostGIS layers

# Offline background maps

Online background maps have to be prepared for offline use by generating vector or raster tiles. Detailed steps on how to do it can be found in Background Maps.

Vector and raster tiles can be packaged in the project. However, as these files can be rather large, it might be impractical to synchronise them trough Mergin Maps. How to work with very large files will show you how to get them in your mobile device.

# Offline PostGIS layers

If you use online PostGIS layers in your Mergin Maps project and need to do an offline survey in the field, we recommend using DB Sync. DB Sync helps synchronising your PostGIS database and GeoPackage layers that can be edited offline using Mergin Maps mobile app.


After setting up an offline project, download it to Mergin Maps mobile app. Then close the app, turn off the internet and open the project in Mergin Maps mobile app again while being offline to make sure that everything works as intended.