Hi Corentin,
> I saw that in London the address of a building is often put as a tag of
> the building. It is the "correct" way wanted by the local community? How
> do you handle multiple address/entrance in the same building? Is the
> "relation:street" used in this city?
I am currently working on the addresses of my vicinity. Even though I'm
not aware of a local convention, I can say that use of `addr:street=*`
is much more popular around me.
> I notice that in London the basement of a lot of houses are also used as
> housing, and they often have address like "22A <name of the street>".
> But I very often see only one address mapped ("22 <name of the
> street>"). Does its existence implicit? Is it a specific tag for this?
Most of the time, building numbers won't have a standard, don't try to
guess [0]. Some examples from my neighbourhood:
[0]: https://www.youtube.com/watch?v=YBbBbY4qvv4&t=4s
1. One building has number 19, the building in the next garden (one
would say that they are completely independent buildings,) has a house
name "The Old School House" but the number is 19 again. This building's
garden has an unused gate opening to another street behind the building.
Next two separate buildings are 19a and 19b. Then comes 21 & 21a in the
same building, 21b in a separate building, 23, 25, 27... So 21a is not
always a basement or any other flat.
2. The close behind that row, has odd numbers on the left hand side,
even numbers on the right. But the numbers start from 5 and 4 so 1, 2
and 3 are missing. Another close nearby has consecutive numbers from 1 to 14
3. Our high street starts with consecutive numbers ('a' and 'b's every
now and then) on the right hand side of the road: 1, 2, 3... all the way
to the end. When the road ends, numbers jump to the other side and
continues back to the start of the road, all the way to 86. So No 86 is
right across No 1.
4. Something Gardens. Road starts immediately with a court with house
name only, "Something Court". It has just a parking aisle in the front.
Then building numbers start with 1, goes on all the way to 20 until
another building with house name only interrupts the sequence. After
that, 21 to 30, then ends with a court with house name only.
5. The road next to this area starts with two floored buildings, divided
into two. One half has 1 and 3, the other 5 and 7. All flats have
separate entrances When two floored buildings end, there are blocks with
three floors. But each flat has a number so 21 to 31 Something Close are
flats in an apartment building.
I note the numbers during my walks, cross reference them with borough's
plans and records, find the missing ones and map. I also use Royal
Mail's postcode finder.
I use `addr:housenumber` to number the building as well as the
`addr:housename` if available. If I know the flats, I add a node to
where the entrance is and add `addr:flats=1-5` [1] for instance to that
node (remember to add `entrance=yes`). If there are two entrances, I add
both and add the flats behind each door. Sometimes buildings contain
more than one number (see #5 above). Then the `addr:housenumber` is
21-31 for example. I add the `addr:street` and `addr:postcode`. You can
add `addr:city`. Postcode is another subject that might be tricky.
Sometimes there's only one building with a postcode and sometimes a
building in a row could have a different postcode than the others in the
same row.
[1]: https://wiki.openstreetmap.org/wiki/Key:addr:flats
> Let say that a house has a basement (under the level of the street), and
> 3 floors. What values should I put in the "buildings:level" tag? 3, 4?
> Are they a tag to clearly indicate this situation?
I add building levels if I remember but don't use them for address
relations. If you want to number individual flats (the ones in #5 above
for example) I think you should add each floor as a building part and
number individually in combination with `level=*`. I'd say I've never
seen this and it is overkill. If you do that, I guess you can use
`addr:floor` [2] but it is not a popular tag and using `level=*` might
make more sense.
[2]: https://wiki.openstreetmap.org/wiki/Key:addr:floor
Along with an in person survey, borough websites/maps could be a good
reference. Also check Royal Mail's postcode finder [3] to see if you're
missing any building numbers or names.
[3]: https://www.royalmail.com/find-a-postcode
Cheers.
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