[OSM-dev] Question: Tags key and value maximum length

Matt Amos zerebubuth at gmail.com
Tue Apr 21 18:01:37 BST 2009

On Tue, Apr 21, 2009 at 12:39 PM, Lars Francke <lars.francke at gmail.com> wrote:
> But MySQL must have a way to save text with more than 255 characters?
> Found it: "Values in VARCHAR columns are variable-length strings. The
> length can be specified as a value from 0 to 65,535. The effective
> maximum length of a VARCHAR is subject to the maximum row size (65,535
> bytes, which is shared among all columns) and the character set used."

i think varchar(255) is more of a historical thing. it is (or used to
be) the default "string" type in rails.

> Well I can put houge amounts of data into multiple tags as well if I
> really wanted. And to 'ban' one thing in the fear of it being misused
> is in my opinion not the right way to go. I don't really want
> unlimited size but an increase to something more sensible.

any limit is going to be arbitrary and the larger the limit the more
people seem to attempt to fill it with rubbish. OSM is primarily for
geographic data, not descriptive text - there are other, better,
systems for descriptive text, such as wikipedia. also, is it really
useful to have all those postcodes for berlin? wouldn't it be better
if each postcode were given its own node (or, even better, an area)
which is more geographically relevant?

> Sorry but I think that is rather...well not the best way to go ;-)

i agree. splitting note or description tags over multiple keys is a
massive hassle.

> I won't nag you any longer I just wanted to register my concerns and
> to provide a (hopefully) valid point as to why a higher limit makes
> sense.

i don't think anyone is saying the 255 char limit is perfect. don't
think that we imposed the limit on nodes because it is a good limit -
we were just making the treatment of node, way and relation tags more

thankfully, now that all the tag limits are treated consistently it
will be extremely easy to increase them in the (possibly near) future.



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