Recent diary entries
Today I was asked by another (very active) mapper via email these questions:
We are currently discussing best practices for landuse mapping in Belgium. Some of the problems:
- do you use multipolygons to avoid overlapping landuse or do you split a residential landuse so you can have smaller landuses ? Or do you just overlay them ? A lot of landuse is already mapped in a rough way, so we typically have large areas of residential landuse.
- Do you include streets in residential landuse or do you exclude them so one can later add area:highway or landuse=highway ?
- I'm in favour of landcover to avoid "forests" in gardens. Which landcover proposal do you follow ? (I believe there are 2).
- what about grass/bushes in towns near highways ?
I wrote some lines how I believe it should be done. Here's a slightly modified version:
Regarding the residential landuse, I am since almost 10 years advocating to not include roads but end the landuse at the property borders. Not only does it add more detail, because you can clearly distinguish (even without roads), parcelled land and common land, it will also be easier to add landuse=highway, i.e. the land that is legally a road. It just makes no sense from a legal point of view to add streets to the residential landuse (save maybe those areas where the streets are private). I do include driveways though, i.e. "roads" on the properties.
Clearly, public roads are road landuse, so they must not be included in residential, industrial, commercial, retail or other similar landuse.
why do people often use huge polygons including whole settlements in one landuse object?
IMHO the 3 reasons for people to include roads are
lazyness (to draw and to determine the precise border, ...)
OSM standard style is not rendering place areas, so people misuse residential landuse to say: built up area
people hating "gaps" or voids in the map and think it must be "complete", so they connect the landuse to the road and prefer to have it "wrong" rather than "incomplete".
Of course it also depends on scale. IMHO we should try to map in a high scale, e.g. 1:500 - 1:1000 (because simplifications can be computed at need, while details can't), but if you do your mapping in 1:10.000 and lower you would likely not represent these details and would "include" the roads (actually it wouldn't be discernable whether they are included or not in these scales).
Using multipolygons in landuse mapping
I also advocate to not use multipolygons for built up landuse, if it is not strictly necessary (never met a situation where it was necessary, but it might exist). It just creates unnecessary complexity and deters less experienced mappers, and leads to errors laters. It is not necessary, just make the landuse as small as you like and need. (I think that landuse is a property of the land, I don't see it as a feature, i.e. for mapping a "residential area with a name" = part of a settlement, I suggest to use place, e.g. quarter, neighbourhood. Can even work for industrial areas (their names)). This way, you don't mix stuff and are not forced to ignore parcels with different landuses which are also a part of the settlement part (toponomastic area).
On the other hand, when mapping in rural areas and landuses like farmland, forests and other natural features (scrubs, heath, beaches, ...), multipolygons might come in handy to avoid duplicating long (and complex) ways by reusing them.
Regarding landcover, I mostly only use 3 values: trees, sand, grass, although it could be extended by more vegetation and surface types (like bushes or whatever term is correct for these, currently I use natural=scrub for thickly vegetated / unpassable areas and avoid the landcover tag there). I admit as long as it doesn't render I still add stupid forest tags additionally, although it really is stupid ;-) I don't know about 2 landcover proposals, but for trees, sand and grass there isn't much to discuss I think.
Grass and bushes along roads
If they are (legally) part of the road I would see them as landuse=highway, grass can be landcover=grass, bushes are (in my mapping but I believe it is a common agreement) natural=scrub.
I believe the local people usually know where the centre is. They tell you when you ask them. Give it a try, I bet you'll see that you get similar answers.
I would expect this most central spot to be often in front of the townhall (maybe sometimes the cathedral) or the main market square (in traditional towns) or likely both. Maybe the train station can be such a center as well (in more recent towns which developed after the railway was invented).
One criterion could be: where would you go to protest something. If you were to gather together with "all" citizens, where would you go.
Streetsigns aren't useful from my experience. Often the centre is inside the main pedestrian area (typical for Germany, where many historic city centres have been pedestrianized) and it is generally so big that you will get signs in the outskirts indicating "city centre", but when you arrive there will not be a sign stating "this is the city centre", the signs will simply stop indicating a centre when you are in a central area (they might indicate "all directions" now, but that's a different story, maybe to be told another time).
In special cases there could even be several centres, e.g. Berlin (there might be a bit of a difference between big cities and smaller towns). For West-Berliners, the centre was likely Breitscheidplatz (in OSM) and as you can see it is also very close to the former main station of West Berlin, Bahnhof Zoologischer Garten).
For the people in East Berlin it was probably Alexanderplatz (in OSM) with the centre extending also to here (between tower and main town hall. There might be some other opinions because the former centre (castle) was also reclaimed by the officials, naturally (see below). This is Alexanderplatz, you can also see the prominent tower, visible from everywhere in the city. Huge towers are generally issueing a statement of centrality). There's also a station, but it is not important as a train station (it is a very important underground station though, with 3 lines crossing):
Berlin central island
Another central spot and maybe the official centre during the GDR, surely during the German Empire, is the palace (Stadtschloss) (now in reconstruction), (in OSM), in times of the GDR this was the place of the "palace of the republic" (Palast der Republik), at its side there is also the national council.
In this map from 1688 you can see the central island (yellow-green). By that time there were still 2 towns, Berlin (purple) and Cöln (yellow), and this origin is likely a reason that there's some concurrency between Alexanderplatz and the castle. The castle is signed a. Alexanderplatz is in Berlin, while the castle is in Cöln.
The Berlin castle 1900
After tearing down the castle and waiting 20 years (in the meantime they set up a permanent grandstand for their military parades on national holidays), the palace of the republic was errected (after the reunification, the Germans waited again 20 years, until they decided to demolish this "palace" and reconstruct something which imitates the imperial castle's volume and facade).
Tearing down the castle, 1950
Grandstand for parades at the place of the former castle, 1952 (likely not perceived as a centre):
Palast der Republik, 1981:
Closeup of a parade in front of the Palast der Republik, 1978:
Palast der Republik from the inside, 1976
Here's another map to illustrate that this is the centre of the centre (also note how the avenue "Unter den Linden" points straight to the castle (=centre), for many kilometers, and bends right in front of the centre to pass the castle). In red the former castle, gray underneath the palace of the republic, to the north-east Alexanderplatz and its tower):
The current reconstruction called Stadtschloss, (2015). Very visible how Unter den Linden bends for the castle, see it also in a much bigger scale in OSM. This is the main road, leading straight to the castle (current federal road does not completely follow the old road, but I think you can get it) and at the time used by the king to got to his residence in Potsdam. What is now there is in part also result of more recent times: the Nazi plan by Albert Speer).
The OSM crowd currently has set the centre a bit closer to the west, at the crossroads Unter den Linden and Friedrichstraße (in OSM), it's not completely off as this is a very central place (and in the historic parts of Berlin, pre-industrialization), but it isn't a centre where you would go to gather for protest (these would be Pariser Platz in front of Brandenburg Gate and close to the Reichstag, or Alexanderplatz).
I will soon have a look how this node moved around in OSM with the years (and also look for the previous Berlin node that was deleted in 2008).
There a very useful feature in JOSM which I just discovered now: when looking at the history diffs of an object and you choose the coordinates tab, you get a map visualizing the geometry in a map.
From time to time people are moving the Rome node.
I found it interesting to see how the position changed by the time. This is the complete position history of the Rome node:
The node creation on 2007-10-15. Back then the local map was empty and a node anywhere near the centre was perfectly fine, but the editor decided after 10 minutes he could do better and already refined to a location close to where the central point commonly is associated with (the Campidoglio).
A further refinement on 2007-10-22. Now the position is perfect (for our means), it indicates the centre of the Campidoglio with the equestrian statue of Marcus Aurelius.
This is the Piazza del Campidoglio with the equestrian statue in the centre, you can also note the concentric pavement structure indicating the centre:
Now comes a longer period of people "touching" the node without actually changing it noticably. Take a look at the distance indicator:
Until someone comes along and decides in 2011 to relocate the centre close to the Spanish Steps (although this is a famous place, it is not generally considered the "centre point":
Just one minute later, the same user slightly adjusts the position, but keeps it at the Spanish Steps (Piazza di Spagna):
6 months later I relocate the node to the Capitoline Square (Piazza del Campidoglio):
3 years later another user starts readjusting the exact position (maybe in an attempt to optimize the rendering label positions and reduce label omissions):
Some months later, the node is moved further away from the center to the border of the square:
3 months after this, there's a new significant relocation, this time to Piazza Navona (while it is an important place, it is not the "centre"):
The same use relocates the node, 2 months later, to the Piazza delle Rotonda (square in front of the Pantheon):
That's where we're still right now, but I think I will relocate it to where I believe it belongs and where most of the other mappers also have seen for it the place to be. Well, actually there's another spot which might be brought into discussion as well: it is the place of a column just a stone's throw away on the Roman Forum, close to the temple of Saturn, errected the Emperor Augustus, which is the official start point of the "Vie Consolarie" (main arterial roads, historically until today).
Just discovered this POI, someone offering lessons in mathematics and accepts bitcoin. Apparently he is living in the middle of the street: http://www.openstreetmap.org/node/3197308571