[talk-au] [OpenStreetMap] intersections

Stephen Hope slhope at gmail.com
Wed Nov 30 07:16:08 GMT 2011


On 29 November 2011 23:53, Richard Weait <richard at weait.com> wrote:

>
> Having a place tag is good, having a population tag is good.  "Faking"
> either of those for the renderer or otherwise seems bad.



We're talking about hinting, not faking.  Marking something as a city when
it's not, that's bad. Having a specific tag (that the renderer can ignore
if it wishes) that says this thing is more important than you might
otherwise think is not faking, it's adding information.

Sparseness is actually one of the edge cases that's less important, in my
view.  But even there, I bet you can't create an algorithm that will behave
as well as good human mapper, though we can probably do one that's good
enough.

But the more important use for hinting is the case where you have a bunch
of similarly sized items fairly close to each other, and in every computer
readable metric they have similar results. So the renderers pick one at
random and place it, hiding the others.  The problem is they almost always
pick the wrong one. If there is one internationally famous place surrounded
by a bunch of similar places that no one has ever heard of, with only room
for one on the map, it's almost never the expected one that shows up.  But
it doesn't even have to be that important - near me is a set of suburbs
that are all about the same size and population, but the one that everybody
would expect to see on a semi-zoomed out map is not the largest, or the
admin centre, or in the middle, or famous outside my city - it's just the
oldest, the one that's been around while everything else was farms. All the
other suburbs near it have grown more recently, and they are mostly larger
population, have better shopping, etc.  But when somebody talks about the
area, it's always the oldest one whose name they use. Weather reports,
traffic radio, everything. This is not the stuff a computer is going to be
able to figure out without a hint.

I can think of many other examples of similar issues just in my city.  Zoom
in far enough, and all 60+ suburbs should show, no question.  But if you've
zoomed out enough that we can only fit in about a half dozen names around
the city area, pretty much everybody would give you the same list of which
ones they should be.  All the suburbs are equal, but some are more equal
than others.  And if we're going to make good, usable maps, we need to know
that.

Stephen
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