Last Saturday was the start of a bit of a heat wave here in London, and we were making the most of it with a BBQ in Derick's back yard. The first of the OpenStreetMap Meat-ups:

We sat and talked about the heat and the meat and the maps, and it was glorious!

Derick set us a small mapping challenge, and since I had accepted the challenge, and since it was a very small mapping challenge, I felt guilty about not bothering to do it, so while staggering home drunk with the girlfriend, I popped over to my slice of the cake and took a few blurry photos of that row of shops. I haven't actually entered this data in yet, but this shop POI mapping reminds me of something...

I was meaning to post this diagram a while ago. Some photos of shops are rammed full of information which can be read off and put into tags. This is a nice example of that:

Fundamental point about this: Some tags are more important than others. Clearly it's quite tedious to key in all of these tags. You're still making a very valuable contribution to OpenStreetMap if you just stick in a node with the 'amenity=restaurant' and 'name=Med Cafe'. Everything else is a bonus, and skipping over the details is a perfectly valid way of mapping more rapidly.

Now there are some diverse opinions about tags to use for some of these things, and I'm unlikely to persuade any keen POI mappers that I am right and they are wrong, but if you're new to POI mapping then you could do worse than use the tags as illustrated above. After all I am right. :-)

First of all, why is it amenity=restaurant and not amenity=cafe? Well in this respect this photo is an atypical example, but perhaps that makes it a useful example. Categorising POIs can be a tricky business, and quite subjective. You should look at what the primary function/characteristics of a POI are, and make a judgement. Do not necessarily allow your judgement to be swayed by the name. In this case it's a funky soho establishment where they've gone for a funky 'cafe' in the name, but I judged that it's much more of a restaurant than a cafe. That's fairly common. Another example of this is all those north London convenience stores which call themselves "something supermarket" when clearly there's nothing "super" about them.

Another thing you should not do is tag it 'amenity=restaurant;cafe'. If there's a place for semi-colon value separators then an amenity tag is not it.

I use 'phone' rather than 'contact:phone' because that's what most other mappers do. This is no coincidence. It's simpler. I generally disapprove of most proposals to introduce "namespaces". While they have the feel of something nice and rational and organised, that comes at a price. Tags are supposed to be simple. We're not developing a programming language here. New mappers have to learn to type these things in and remember them. The 'contact:' prefix offers very little real benefit but makes a tag much less simple.

Regarding phone number format, I tend to slap in the phone number in whatever format I see on the signage, rather than converting to some sort of standardised "+44" format. That's a speed of input thing. Phone number formats make my head hurt so I don’t even try to think about it while typing them in. This might screw over a system which tries to dial the number, but really, if a system fails on that, then it'll always have problems eating OSM data. That said, I have absolutely no problem with somebody "correcting" that data later.

Websites are quite fun. I think these could be quite a neat way of enriching the data set. Clearly it should be 'website' rather than 'contact:website' for the same reasons as above. Sometimes I stick it in the browser to check if the website actually exists. This also makes it easy to put the full 'http://' in front. Sometimes I don't bother.

The same applies to 'postcode, but you may then be wondering why I use namespaced tags for the other address bits. I suppose I could use 'housenumber' instead of 'addr:housenumber' and indeed I do prefer the simplicity of that, but there's a history behind this one. A lot of longwinded discussion and debate around address tagging took place years ago. Lots of ideas for different edge cases to accomodate and ways of representing things. Eventually the guys in Karlsruhe went out and mapped, and then came back and fed back their experiences of a tagging scheme which seemed to work: "Karlsruhe Schema". Looks like Marcus Wolschon did this back in April 2008 and started the wiki page with the wonderfully pragmatic: "This schema is used for first tests of tagging house-numbers. You may use or ignore it. It can be changed at a later time after everyone has gathered experience with tagging house-numbers and interpreting the mapped data." That formed the basis of what we now see on Key:addr, and most mappers now follow it. From a personal perspective I find address mapping deeply uninteresting. I'm quite happy to go with the majority on this one. In fact I often skip these tags anyway (particularly addr:street). If typing in awkward tags is taking too long, don't let it put you off mapping. Just skip it!

So that's the way I do some tagging. If you disagree with me, commence criticising comments. Or if you really feel strongly, head into my territory and change my tags. This Saturday is the perfect opportunity:

The second BBQ meet-up round my house will be this Saturday. Last weekend it was meat-tastic, and this one will be no different:

I'm sweating as I type this, so let's hope the heatwave lasts until Saturday. I live up in North London near Archway tube. If you haven't heard of Archway, that's not because it's a mysterious outer london location. It's in zone 2! It's just not well known because it's a bit crap. All the details and instructions are on the wiki, apart from those details which are hidden on facebook somewhere. But yes... All OSMers welcome! There will also be a number of non-map-obsessed friends and family present, so I expect you all to be on your best behaviour.