Free Map Limits
The Ordnance Survey has provided limited free access to their maps and data since 2007. Google maps and France's IGN have similar arrangements. The free services are meant for non-commercial, low-volume hobby sites like this one. So if my monthly map quotas get exceeded by too many users then you may have to wait until the next month when the quotas are renewed again.
All the map providers are keen to get site authors like me to upgrade to commercial services which I would then have to somehow ask site users to pay for. I have no wish to make a business out of this, nor even a paying hobby, so I won't be going down that route. But I'm open to any legal ideas to keep the site free for regular users. It's been suggested that I could allow users to upload their own developer API key and use that to produce the maps instead of my key. That would certainly work but I'm not totally convinced that's in keeping with the spirit of the free licenses. The keys are meant for developers after all. Feel free to email me at firstname.lastname@example.org if you have any thoughts about this or any other ideas.
Finally, let me emphasize that the map usage here is fully legal and is directly supported by all three map providers. I once read a snarky comment in a cycling forum implying that this site was somehow cheating the map providers out of income by providing dodgy stolen map features in some mysterious underhand way. That stung because it's not even a tiny bit true. The poster could have verified the legality of sites like this with about ten seconds of Googling before posting, but hey, that's random strangers on the internet for you. As ever, xkcd has it covered.