OpenStreetMap: the free map of the world

Almost every map PlotMyMap makes comes from OpenStreetMap, a map of the world made by volunteers. This guide explains what it is, how it is organised, how it can be used and how to improve it.

What OpenStreetMap is

OpenStreetMap (OSM) is a geographic database of the whole world, free and editable by anyone. It was born in 2004 in the United Kingdom, when Steve Coast, tired of official maps being expensive and closed, started mapping London with a GPS and a bicycle.

Today millions of registered people edit it, and several tens of thousands do so every month. There is a bit of everything: residents adding their street, hikers uploading their routes, councils and companies contributing data, and humanitarian teams mapping areas with no map after an earthquake or a flood.

The idea is Wikipedia applied to maps: nobody owns the whole, anyone can fix what they know and everything is recorded, with its history of changes.

What is inside

OSM is not an image but data: points, lines and areas with tags. A street is a line with tags such as “highway=residential” and “name=High Street”; a building, an area with “building=yes” and, if known, its height or number of floors; a fountain, a point with “amenity=drinking_water”.

That means it can be drawn in a thousand ways. The map you see on openstreetmap.org is just one of many possible styles; the same data serves a car navigator, a cycling map, a hiking app or, as here, a line drawing.

OSM is strongest on streets, tracks and footpaths, often more complete than in commercial maps; on buildings, in cities; and on a huge variety of details: fountains, benches, viewpoints, shelters, ruins. The most uneven part is coverage: in Europe it is excellent almost everywhere; in some rural parts of the world, still sparse.

Names are stored in the local language and often in others too. That is why a map of Tokyo or Athens can be labelled in the Latin alphabet: PlotMyMap uses the Spanish or English name when there is one.

The licence: free, with attribution

OSM data is published under the ODbL (Open Database License). It can be used for any purpose, commercial included, on two conditions: credit the source (“© OpenStreetMap contributors”) and, if you redistribute a modified database, share it under the same licence.

A map drawn from that data, such as a poster or an image, is a “produced work” and can be used freely as long as it carries the credit. That is why every PlotMyMap map has it written in a corner. If you crop the map or publish it, make sure the credit stays visible or appears next to it.

In Spain, PlotMyMap adds buildings from the Spanish Cadastre and relief from the Instituto Geográfico Nacional, which are also open data with an attribution requirement; elsewhere, relief comes from SRTM and general coastlines from Natural Earth. All of that goes in the map credit too.

Using the data without abusing it

OSM runs on donations and its servers are modest. Its policies ask heavy users not to download data on demand from those servers, but to keep their own copy.

That is what PlotMyMap does: it downloads data by region from Geofabrik, a service that distributes daily copies of OSM by country and region, stores them on its own server and refreshes them from time to time. The site's background map and place search are its own too.

The practical consequence is that a change you make in OSM today takes a while to show up in your maps: as long as it takes for the next update of that region to arrive.

How to fix a mistake, step by step

If your map is missing a street, a path is wrong or a name has a typo, the best thing is to fix it at the source: then it is right here and in every application that uses OSM.

1. Create an account on openstreetmap.org. It is free and only asks for an email address.

2. Find the place and zoom in as far as you can. Press “Edit”: this opens iD, the site's own editor, which runs in the browser with nothing to install. The first time it offers a ten-minute tutorial that is well worth doing.

3. Make the change. To fix a name, click the street and change the “Name” field. To add a path, choose “Line”, draw it over the aerial photo and say what it is (footpath, track, street). To move something, drag it.

4. Save with a short description of what you did (“Added path to viewpoint”, “Fixed square name”). The change is published at once and anyone can see and review it.

If you would rather not edit, you can leave a note on the same site: click the spot, write what is wrong and a local volunteer will look into it.

Good habits

Map what is there, not what you would like. OSM records reality on the ground: a private road is tagged as private, not deleted; a street that exists only in a plan is not drawn until it exists.

Do not copy from other maps. Google Maps and most commercial maps are copyrighted; copying from them is forbidden. The aerial imagery offered in the editor is authorised, as is anything you have seen or measured yourself.

Start with what you know. Your street, your neighbourhood, your village or the trail you walk every Sunday. That is where you can contribute most, and within a few weeks it shows.

And if you make maps with PlotMyMap, every improvement you make in your area appears in your next map. Few drawing tools let you fix the world before you draw it.