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ArcGIS Pro

QGIS Offline And In The Field

Mergin Maps – Offline Data Collection for QGIS Projects

The guest for this episode is Peter Petrik, the CPO of Lutra Consulting. He previously worked in the automotive industry before transitioning to geospatial about eight years ago. Ever since joining Lutra Consulting, he has made use of his programming knowledge and skills, while collaborating with others to develop products and contributions to the open geospatial community. One of their recent developments is Mergin Maps, an open-source software that allows users to take QGIS to the field.

What Is Mergin Maps?

Mergin Maps is an integration that allows users to collect geodata using their mobile devices or tablets. Teams working together can use Mergin Maps to synchronize their data seamlessly to the cloud, or a server. The QGIS plugin enables users to easily access their data in the cloud, and utilize QGIS to post-process or analyse their project.

How Mergin Maps Works

In order to use Mergin Maps to conduct field surveys for a QGIS project, the first step is installing the Mergin Maps Plugin for QGIS. The plugin will ‘package’ your whole project into a folder, and make all of its layers available for use offline. If the project uses an online map, QGIS processing tools can be used to generate its layers for offline use. The plugin also runs several validation checks to ensure that the tool will work correctly on a mobile device. Once everything is set up, a single click on the synchronise button will take the project to the cloud. The project can then be downloaded to a mobile device, and used offline within the Mergin Maps Input app.

Every time a user clicks on the sync button in the app, any new changes are pushed to the cloud, and a new version of the project containing those changes is created in the cloud. It is easy to track the changes made to the project and identify the user that made them.

Mergin Maps also has an automatic merging feature. Users working offline on the same project, will have their data automatically merged by Mergin Maps once they sync it to the cloud. This removes the need to do it manually, and can save a lot of time if there are many users in the field. Mergin Maps does not have restrictions on the number of users that can be added to a project.

Data Storage When Using Mergin Maps

Mergin Maps is open source, so users are not restricted to using just its cloud. Users may opt to deploy their own servers to store their data.

The Mergin Maps Cloud is an option for users who do not wish to have the weight of server infrastructure and maintenance on their shoulders. There are various Mergin Maps subscriptions for users depending on their storage needs. For academia and personal use, Mergin Maps is free to use for up to 100 MB of storage.

Mergin Maps has features that help users reduce the size of their data, and cut down their storage needs. For example, there is a QGIS tool where users can set the resolution of all the photos captured in the i.e. 1 MB via the app. This helps to avoid storing high resolution photos whem they are not necessary.

Mergin Maps User Management

Mergin Maps allows a project owner to manage the users that can participate in the project. A user can be added to a Mergin Maps project as a reader, writer, or administrator.

Readers can only access the project and view the data, while writers can create new versions of the project, either in the mobile application, or from QGIS. Administrators can invite other users, as well as change user permissions.

Each user will need to create a Mergin Maps account before they can be added to a project. Once they have an account, they can use the same log in credentials to sign into the mobile application and, download the project from the cloud onto their device. They can then start working in the project (i.e. digitise, edit data, syncing etc.)

What Expertise Do You Need to Use Mergin Maps?

For the Mergin Maps QGIS plugin, some knowledge of GIS is required to be able to set up a project and push it to the cloud, and later access the data and do analyses and generate reports.

No GIS knowledge is required for users of the Mergin Maps Input app. The developers acknowledge that the users of the app are likely from different fields, with varying levels of knowledge. Therefore, they kept the design simple and easy to use. On average, a new user can learn how to use the Mergin Maps Input app in about 15 minutes!

Mergin Maps is flexible and has plenty of users from various industries and applications including agriculture, utilities and fibre optic companies, consulting firms, and many more.

Mergin Maps Integration with External GPS Tools

If the location from a mobile device is not very accurate, a user can connect to an external GPS. Mergin Maps supports most of the common external GPS tools which a user can plug in or simply connect to. They will then be able to use the external GPS’s precision for their data collection. Only Android is supported for this functionality at this time.

Controlling Data Inputs on Mergin Maps

Mergin Maps offers a number of widgets that can be used to control the values accepted by the Mergin Maps Input app.

For instance, if an input field is set to only accept integer values, an integer widget will appear on the data collector’s mobile device as a slider, or text box where they can only input a number.

Further limits can be set to define whether the number must be positive, or may not exceed a certain figure. For dates, a widget will pop up on the mobile device as a calendar. These functionalities are great for helping to manage data quality and data assurance standards. 

There are also widgets for lists, checkboxes, and other common widgets and constraints. Users can also use the QGIS Expression Engine to write calculations for derived fields.

There are lots of possibilities supported on both the QGIS plugin, and Mergin Maps Input app, where users can apply some basic quality assurance methodologies, and help with capturing quality data in the desired format. After data has been pushed to the cloud, users can make use of the Python integration to write scripts in QGIS, or on their server to further validate the data from an input field.

Mergin Maps Community Edition

Mergin Maps are advocates for open-source GIS and that reflects in their products. Their users are not vendor locked within Mergin Maps infrastructure. If a user is tech-savvy enough, they can set up Mergin Maps, and use it on their own. There is a public GitHub repository with a Docker compose file that users can run for themselves for their personal projects. In case they encounter problems, they can join the Slack chat and seek help.

Mergin Maps Enterprise Edition

The Enterprise edition is best suited for companies that need to hold data in their servers due to legal or security reasons, or internal rules. Mergin Maps facilitates this by offering their knowledge from their years of experience running cloud services, to help in the deployment and maintenance of each company’s server, making sure everything works smoothly and efficiently.

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About the Author
I'm Daniel O'Donohue, the voice and creator behind The MapScaping Podcast ( A podcast for the geospatial community ). With a professional background as a geospatial specialist, I've spent years harnessing the power of spatial to unravel the complexities of our world, one layer at a time.