[OSM-newbies] Update Drawing Guidelines (Editing Standards and Conventions)

[Helge Hafting]

Hagen Riedel wrote:
> I think it is very important to update the following site: http://wiki.openstreetmap.org/index.php/Editing_Standards_and_Conventions.
>
> For myself as a newbie it is important to see some examples and have some guidelines. Even more it does not make a good impression if new users are linked to an out-of-date information site.
>
> In my opinion the page should answer the following questions:
> Can I already use proposed features?
>   
You can use any tag you want to - but only tags used by more people will 
be useful.
Consider voting for the proposed features you want to use - that way 
they become
"official" faster.

Instead of just making up a new tag -  propose it. anyone can propose 
new tags.

> How accurate one should map? How many points roundabouts 
A roundabout needs at least one point per connected road - and at the 
very least three.
Many roundabouts are made with 4 points. Feel free to use more - *if* your
pretty roundabout is accurate. I.e. don't make a 12-point roundabout
if all you have is 2 gps points at the location. You can get accurate
roundabouts by going all around in the outermost lane with a good gps. Don't
do this when there is heavy traffic though. You can get accurate connections
by driving in and out each connected road. Sometimes the connecting roads
split into an Y-shape as they connect. If you map such detail, use the 
oneway
tag appropriately so navigation software won't think there are
twice as many exits.

How much work you put into this is up to you. The 4-point roundabouts are
sufficient for navigation purposes. Elaborately mapped roundabouts with
12-16 points and Y-shaped connections look slightly better when you zoom
in a lot. Josm has a tool for turning a set of points into a perfect 
circle. After using it,
reposition the roundabout by dragging, as it tend to get offset.

Remember that roundabouts are directional - don't make them the wrong 
way around.
> and slopes should have at least/most? Is it best to use as few as possible points with straight ways? 
If the road isn't straight - don't make it straight. Be aware that gps 
has limited precision.
So don't bother forcing the road to follow your gps track withing 0.5m 
precision. The data
isn't that good anyway.  Still, a road with sharp turns may need points 
with 2s distance
or so in the turns. You can get away with a lot less in wide turns and 
almost straight
sections. To put it simple, the straight pieces you make shouldn't  be 
further
away from the stripe of gps points than the gps precision. And it is 
usually a good idea
to do better than that too. GPS may be 10-20m off, but that error is 
almost the same
for many points. The shape of the road (points relative to each other) 
has higher
precision, and it is nice to preserve that. If the road consist of a series
of slight curves (road in the hills/mountains) then it is useful
if each curve actually is on the map. People can then use
instructions like "third left curve after the intersection."

> Is it recommended to use overlapping ways (car, tram, bike)?
>   
Usually not - josm will even warn you about it because it is usually a 
mapping error.
car+bike: make a car road, and add cycleway=lane (if there are bike lanes)
or bicycle=yes. A cycleway next to the main road can be mapped separately.

The tramline may overlap - if cars really drive in the tram lane. If not,
perhaps it is a dual carriageway with a tramline in-between?
> How to make nodes aligned in pairs (separated highway)?
>   
Drive down both ways - then your gps will log two lines.  Make both roads.
Set down the nodes in pairs, that way the road-road distance will be
constant even in turns. Like this:
*-------*-------*
*-------*-------*

Not:
*-------*-------*
----*------*--------*


> How areas should be tagged (adjacent or with space between)? Mark big buildings or just the outline of residential areas? How to tag towns and its suburbs? Is it sometimes good additionally to add a point, e.g. with parking areas?
>   
Add anything that you _can_ add. My gps isn't accurate enough for 
small/medium buildings. Large
buildings are often tall too - creating other problems if you go too 
near with a gps. Of course there
are other tricks, like satellite images or measuring distance between 
walls and roads.

Also, bear in mind that you don't _have_ to map everything you _can_ 
map. Getting the
roads, cycleways and parking lots are probably more useful than the 
buildings. Buildings are
a bonus - I can plan my shopping trip even if all I see is the road, the 
parking lot and
a shop node. I will assume that there is a building there. :-)


Many questions can be answered by looking at the work of others. Download
pieces that are very well mapped and have a look! Note that some countries
have different standards - preferably look at your own country.


Helge Hafting