Republishing this episode because of the audio issues with the original episode!
Mergin Maps lets you create QGIS projects that can be used to collect and edit data in the field. You see updates in near real-time, even from the field. Works offline. Edits are merged automatically. View and edit geodata in the field. Integrate with existing GIS infrastructure using open formats.
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In Conversation
From the Automotive Industry to Open Source GIS
Daniel: Peter, welcome to the podcast. You’re with Lutra Consulting, and today I want to talk about Mergin Maps. Would you introduce yourself and tell us how you got involved in geospatial?
Peter: Thank you for having me. I’m Peter Petrik, and I got into geospatial about eight years ago at Lutra — it’s a lot of fun to do open source and GIS together. Before that I was in the automotive industry, developing numerical solvers for combustion systems. It sounds a long way from maps, but I studied physics and numerical methods, and I worked in QGIS on the mesh data layer, where you use those simulations for modelling things like floods or meteorological data. The physics is the same everywhere — it just depends where you use it. I develop mostly in C++, Python and C.
What Mergin Maps Is
Daniel: What is Mergin Maps?
Peter: Mergin Maps is a way to collect field data with your mobile or tablet easily and collaboratively with your team, and then synchronize it seamlessly to the cloud or your server, and from there to QGIS, where you can use all the QGIS features to post-process or analyze the project. It starts with a QGIS project. If you already have a QGIS project you want to use in a field survey, you install the Mergin Maps plugin for QGIS and use the packaging system — it packages everything to a folder so all your layers can be used offline, and does a bunch of validation so you can be sure it’ll work correctly on your phone. Then you click synchronize, it goes to the cloud, and on your mobile you install the Mergin Maps Input app and synchronize back.
Daniel: What about online layers, like a base map from OpenStreetMap?
Peter: The mobile application uses the same rendering engine, the QGIS core library, as your desktop QGIS — so it’s really the same QGIS running on your mobile with a slightly different user interface. If you have an online map in your project, you can use it as-is on the mobile, but then you need to be online. Or you can use QGIS processing tools to generate an offline map from your online map, and then it can be used offline without an internet connection. You can use map themes to switch between online and offline — it’s up to you.
Versioning and Automatic Merging
Daniel: When you click sync, what actually happens, and what makes a new version?
Peter: The packaging is really a series of validations — it makes sure your survey layer (we prefer GeoPackage) is in the same folder and flags settings that won’t work on mobile. When you click sync, it takes the whole folder and pushes it to the server — either your own server, since we’re all open source and you can deploy the server Docker container yourself, or our cloud. The technical background is similar to git. Every time you change something — add a few points, modify attributes — and press sync, it makes a difference between the original file and your modified file, and that difference is sent to the server. One version is a set of changes sent in one batch. It also does automatic merging: if you have 10 users in the field, all offline, and they all synchronize in the evening, it automatically merges the data from all 10 sources. You can make an audit log to see who did what change, when. You can even think of it as a versioning system if you don’t want to set up PostGIS — just use Mergin Maps to version your QGIS project or GeoPackages.
Storage and the Input App
Daniel: Is there a size limit to projects in the cloud?
Peter: My project is a few gigabytes and a few thousand versions, and it works nicely. The only limit, if you use our cloud, is the storage in your subscription plan — and that storage is for the latest version, not the whole history. We also have tools to reduce storage size — for example, a tool where in QGIS you set that you don’t need full-resolution photos, so the mobile app automatically reduces photos to, say, 1 megabyte. Or you can run a Python Docker container that moves photos from the cloud to third-party storage like an Amazon S3 bucket and patches your QGIS project with a link. The Input app runs mainly on Android and iOS — phones and tablets — and we’re developing Windows and desktop versions. It has no strict hardware requirements and is optimized for small mobiles; the main limitation is having enough storage on your phone for the project.
User Management and Field Volunteers
Daniel: If I have 15 freelancers doing field work, do I just send them my login?
Peter: I would not advise that, because then you won’t see who did the change — it’s the same login. There’s no restriction on the number of users you can share a project with, so the best way is to ask them to create Mergin Maps accounts, then add them to your project as writers, readers, or administrators. Readers can view the data, writers can create new versions from QGIS or mobile, administrators can invite others and change permissions. We have many users doing it this way — for example, a GIS consultant maintains a project and has 20 or 40 volunteers who just install the app and go around the forest collecting data about trees or animals. There’s a case study from a wildlife trust in the UK doing exactly that, and a citizen project in the Netherlands where people fill in forms for archaeological discoveries. The Input app is a simplified version of QGIS on your mobile — we keep it very intuitive, so you can learn it in about 15 minutes without any training.
Controlling Data Quality
Daniel: Does my mobile device’s GPS limit accuracy, and can the app use an external GPS?
Peter: Yes, we support most external GPS units — you plug it in, connect to it, and it uses the external GPS precision. For many applications, though, the few-meters precision of the phone under clear sky is fine. In QGIS you set up the form for what’s editable and what values are accepted — for an integer value you use an integer widget, which appears as a slider or number field on the phone; for dates a calendar pops up. You can set constraints — a number must be positive, or not bigger than 100 — and use lists, checkboxes, and the QGIS expression engine for derived fields. You can use tabs so that additional info only shows if a checkbox is checked. It brings back quality data in the format you want, with basic quality assurance already, and afterwards you can use Python integration to write scripts that further validate the data.
Who Uses It, and What’s Next
Daniel: Who is using this commercially?
Peter: Plenty of users from various industries — electricity utilities, fibre optic companies, GIS consultants doing field surveys, agriculture. We have a case study from South Africa where a farmer records the weight of pecan nuts for each tree and soil composition. For a fibre optic company, they use the same QGIS project for high-level design, detailed design verification, recording deviations during implementation, and then asset management — it’s as flexible as QGIS itself. In the long term we want to integrate web map overviews into the Mergin Maps cloud, so when you get a new version you can instantly see a web map, the same graphics as desktop, and share it with your client to see progress in real time — that should arrive late this year or early next. We have a community Slack channel where we discuss new features with our users.
Daniel: Can I run all this myself?
Peter: Yes — there’s a public GitHub repository with a Docker compose file, so you can run it yourself for personal projects. For a production-ready company deployment you need some server and Docker knowledge. We’re very much in the open source GIS world — no vendor locking — so there’s always a Community Edition you can set up on your own. We also offer an Enterprise Edition for big companies that need data on their own servers for legal or security reasons, which comes with help with deployment and maintenance. To learn more, start at merginmaps.com, or join the community Slack channel — there are over 400 users there already.
