My in-house application is using the OpenStreetMap tile servers {a-c}.tile.openstreetmap.org for a 'free' base layer. I've read the tile usage policy and although it prohibits "heavy use" it only provides a vague reference to what this might be.
Users within the company office periodically see a slow down in tile performance (e.g. suddenly each tile takes 10 – 15 seconds to download). This happens for map areas they use on a regular basis (it's unlikely the tiles are being generated on-the-fly) and it doesn't happen for remote users (who access the tile servers from a different origin IP). This suggests that the tile servers are throttling performance based on origin IP.
I found some source code in the OpenStreetMap Github mod_tile repo that supports throttling based on IP but 1) I'm not sure if this is what is used at {a-c}.tile.openstreetmap.org and 2) I still have no idea what the usage limits are.
Are there defined and published limits on how many tiles per (day|week|month) a single IP may request?
Best Answer
Even if there are specific limits they can change any time. Also specific applications/users might get blocked explicitly if they put too much stress on the servers, independently of these limits. Remember that the goal of OpenStreetMap is not to provide free map tiles for everyone. OpenStreetMap is about free map data.
The Tile Usage Policy you mentioned suggests to contact the system administrators or to ask at the OSM IRC channel. This is either #osm or #osm-dev at irc.oftc.net.
If your company needs to access lots of tiles then consider running your own tile server.