TopPlusOpen and aerial photos offline: official maps

Since 2017, Bavaria has had half of its land photographed from the air every year. The photos become aerial images at 20 cm per pixel, and anyone may use them, commercially too, as long as the source is named. Fifteen of Germany's sixteen states do the same. The federal government adds a topographic map of the whole country: TopPlusOpen, from the Federal Agency for Cartography and Geodesy (BKG).

For a hike, these are two maps beside the familiar one drawn from OpenStreetMap: a second map to check a path against, and a picture of what is really on the ground. This post is about what they show, what their open licences allow, which credit goes with them and where they stop. walker, the walk, hike and ride tracker I make for Android, downloads both for areas you choose on the map. How it does that comes near the end; everything before it holds for any app, and for a map cut-out in your own hiking blog.

What TopPlusOpen is

TopPlusOpen is BKG's web map. It covers the whole world, gets finer over Europe, and goes down to a town map for Germany and the areas along its borders, in 19 zoom levels. BKG updates it once a year, and the data in the service date from August 2024. It is under the "Datenlizenz Deutschland – Namensnennung – Version 2.0", the German government's open data licence with attribution, dl-de/by-2-0 for short, and costs nothing.

What the map is drawn from depends on the state. In eleven states, BKG uses official data alone, the data of the state surveying offices, as its product description says: Berlin, Brandenburg, Hamburg, Hesse, Mecklenburg-Western Pomerania, North Rhine-Westphalia, Rhineland-Palatinate, Saxony, Saxony-Anhalt, Schleswig-Holstein and Thuringia. In Baden-Württemberg, Bavaria, Bremen, Lower Saxony and Saarland, and beyond the border, the large scales are drawn mainly from OpenStreetMap. The left map above shows the split.

If you search for a TopPlusOpen download, BKG does offer the whole map as one archive of tiles. In the projection that map apps use, it is 1.3 TB, which no phone holds. Apps take only the tiles of an area from BKG's map service instead: a server that returns the map image for a given extent when asked.

An official map or OpenStreetMap

Most hiking apps draw their map from OpenStreetMap, the map volunteers keep up around the world. Each has its strengths, and on a hike it pays to know them.

In the eleven states with official data, TopPlusOpen draws what the surveying offices keep in their landscape model, down to the outline of every house. These are the offices that survey the state by law. How good OpenStreetMap is in a given place depends on who mapped it.

OpenStreetMap changes every day, and it records things that matter on a hike. The OpenStreetMap wiki on hiking describes how a path gets its difficulty on the Swiss Alpine Club's scale, how visible it is on the ground, where huts, shelters and signposts stand, and which paths make up a waymarked route. TopPlusOpen is a snapshot instead: even its OpenStreetMap part dates from 23 April 2024, according to BKG's list of sources.

Use both, then. TopPlusOpen shows the land as the survey records it, and OpenStreetMap shows today's paths with their details. Where the two disagree about a path, that is the place to look closer before you set off. The relief, the shape of the hills, walker draws itself from terrain data; how is in contour lines and hillshading on the phone.

The states' aerial photos

The aerial photo under a map is an orthophoto, DOP in German: taken straight down, corrected for the terrain with a height model and true to scale, so it fits exactly under the map. The states publish them at 20 cm per pixel, North Rhine-Westphalia at 10 cm. They are flown again in cycles. Bavaria and Baden-Württemberg renew about half of their area every year, North Rhine-Westphalia every two years. An aerial photo is therefore one or two years old, and two corners of one state can come from different years.

An aerial photo shows what a map leaves out or doesn't know yet: where the forest ends, a clearing, a clear-cut, a farm track, a band of rock. When you choose a way, it often tells you more than any map symbol: how much of it runs under trees, and where it comes out onto open ground, in sun and wind.

Fifteen states offer their aerial photos as open data through a map service, with no sign-up and no key. Mecklenburg-Western Pomerania stamps "© GeoBasis-DE/M-V" into every image, so walker leaves it out. Three services show one fixed year: Berlin 2024, Bremen 2023 and Saarland 2025. Hamburg's service holds a series from 2005 to 2024, and its description lists, beside the city's licence, a closed licence for Pléiades satellite imagery. An app that takes tiles from it asks for one year; walker asks for 2024, the city's own flight. The other services show their newest flight. The right map above shows both.

What open data allows

Most states and BKG use the Datenlizenz Deutschland. According to its text, the data may be copied, printed, shown, changed and passed on, for commercial and non-commercial use, combined with your own data and built into products and apps. The condition is the credit: the name of the body that provides the data, in the form it asks for, the note "dl-de/by-2-0" with a link to the licence text, and a reference to the dataset. If you change the data, you say so.

The other licences are similar or more open. Under "dl-de/zero-2-0" any use is allowed without conditions, with no credit needed. CC BY 4.0 asks for the author, a link to the licence and a note of any changes. Hesse sets it out in law: under § 24 of its surveying and geoinformation act (HVGG), use is free and without conditions. None of these licences rules out an app that is sold. What an app owes is the credit. The same holds for a map cut-out in your hiking blog: you may publish it, with the credit the table below asks for.

The credits come from the description each service publishes, Bavaria's from its terms of use, as of 28 September 2026. Before you publish, check the current version.

The credit for TopPlusOpen

BKG's terms of use ask for a clearly visible credit wherever the map is shown in public. That holds for an app as much as for a map cut-out in a blog. On a website or in an app, "BKG" links to https://www.bkg.bund.de and "dl-de/by-2-0" to the licence text.

The terms tell two cases apart. When an app shows the map straight from the service, the credit is "© BKG (year of the last download) dl-de/by-2-0, Datenquellen", and "Datenquellen" (data sources) may link to BKG's current list of sources. When an app stores the tiles for offline use, "Datenquellen" links to a PDF named with the day they were stored. BKG's example for tiles stored on 8 October 2024 is "© BKG (2024) dl-de/by-2-0, Datenquellen", with "Datenquellen" linking to BKG's file datenquellen_topplusopen_08.10.2024.pdf. An offline map carries the date it was downloaded, so its credit also tells you how old your copy is.

The terms hold one more thing worth knowing: BKG explicitly allows TopPlusOpen to be used to maintain and extend OpenStreetMap, with its own wording for the credit.

Where they stop

• TopPlusOpen is detailed only for Germany and the areas along its borders, and the aerial photos come from the German states. In Tyrol or Graubünden, neither helps.
• Mecklenburg-Western Pomerania has aerial photos, but with a copyright stamped in them.
• TopPlusOpen's data date from August 2024, and an aerial photo is one or two years old. A new path, a closure or storm damage can be missing.
• 20 cm per pixel is too much for a phone. An area of 10 × 10 km at 0.75 m per pixel is about 90 MB in walker. The services also limit how large one request may be (Bavaria to 6,000 × 6,000 pixels), so an app fetches an area tile by tile.
• None of the services states terms for fetching many tiles in a row. An app that does it should do it slowly, and only when asked.

How walker does it

The layers button on walker's map offers four layers: Map (the map from OpenStreetMap), Topo (the same with hillshading, the shading that shows the slopes, and contour lines), TopPlusOpen and Aerial. The map's paths and names lie over the aerial photos, so you can find the path in the picture.

For TopPlusOpen and aerial photos, you tap Download this area. A frame lies over the map, and you pan and zoom until it shows the area. Under it are three levels of detail, 3 m, 1.5 m and 0.75 m per pixel, each with its size, worked out on the phone, so you can choose the detail your phone has room for. Nothing goes online before you tap Download, so no service learns the area while you are still choosing. walker refuses areas over 2 GB. The tiles come one at a time from BKG's service or from the service of the state they lie in, and each download is listed in Privacy & storage. A download that is interrupted resumes where it stopped, so a dropped connection costs only the tiles still missing.

Finished areas are listed in Map packs → Areas, each named by its place, with its layer, detail, size and the day it was downloaded. On the map, walker credits every source whose data are on screen. Tap the line, and Map data opens with the links. For TopPlusOpen that is the credit from the terms, "© BKG (2026) dl-de/by-2-0, Datenquellen", with the day of the download in the link. Settings → Licences lists every state with its licence. How to prepare map regions for the trail is in hiking with offline maps on Android, and the help page has a section on maps.

The line under the map

The credit looks like small print that a licence forces on the map. On a hike it is more useful than that: it tells you who drew the map and which year it shows. If it says "© BKG (2024)" or a state survey office, you are looking at the survey of that year. If it says OpenStreetMap, you are looking at what volunteers last put in. Read the line before you trust the map at a fork in the path.