Misc stuff of me, absolutely unsorted.
Thoughts on stuff
Notes to beginners
So, you want to start to contribute, but you don't dare. Yeah, I had that at the beginning myself, but you'll get over it.
Mapping by surveying
Don't trust your GPS gear too much. Generally I can say: the faster you move, the more correct is your data. Some receivers can compensate the relatively low resolution of GPS by using the Doppler-Effect of the satelite signals. Also generally, if you are quite fast, you're probably in a car. There you have one fixed position for the receivers antenna. The quality depends quite a lot on that.
Get to know your GPS gear. No matter how good or not the gear you are using is (even if you don't use any at all), you can still contribute a lot. But if you use GPS gear, know its limitations. Now how is this possible except by comparison with a map? Well, that one is easy: move along a way you really know (of course with the receiver turned on). Keep your discipline and stay on one side of the way. And then look at the resulting track. You should be able to see how much the recorded track coincides with the way you moved. Repeat this. After a while you get a feeling how much you can trust your gear.
Keep track of everything you encounter. While I was walking around with a more or less homebrewn GPS solution, I didn't really use the track as a base for entries, just as a guideline. But I wrote down everything I saw and created a very rough map on a sheet of paper. Back home I compared my notes with what already existed in OSM. Most of the positions of POIs to enter could quite precisely be deduced from the streets already in the database and my drawings. Okay, some roads were really created from quite insane GPS tracks.
Know reality. Sounds easy? Well, when I look at some entries, this can't be too easy. Roads are built for certain speeds, you will not encounter a hairpin bend in a road that's built for >100 kph. So, roads have bends, some wider, some not. As said above: don't trust your GPS gear too much, in bad reception areas the things will record sudden turns even though you were racing far beyond any speed limits. Always think about the characteristics of the ways you moved along.
Know scale. and Don't be overly precise. If you zoom in close and try to enter a way just like it was recorded, you will end up with a lot of senseless nodes. A road will quite probably not change direction 5 times in 10 meters. But that basically boils down to "know your gear" and "know reality".
We try to approximate reality here. That's basically all of it. Some enter roads without any additional information. I do so often when my recorded tracks show routes that aren't in the database. Most of the time I don't even know what kind of road to enter. Well, I just enter an unclassified road, it's a start. I am convinced that it's better to have a road mapped without details than to not have that road at all. And so maybe someone local or who happened to pass by can add data without having to go there and take a logger with them.
Mapping without surveying
You don't need gear for that. You don't even need gear for most of the surveying.
Trace aerials. Just use potlatch and find an area where the aerial shows a road that isn't in OSM. Enter that road.
Trust averages. Call up an area that is heavily trafficked. You will quite probably see a lot of recorded tracks. And you might even notice that the road in OSM seems to be away from the tracks. Yes, not everyone who uploads tracks corrects the OSM data. Just try to find the highest probability for that road. Often a road is entered into OSM by one person with a low reception GPS gear and never corrected afterwards.
Don't overly trust aerials. If you find a road where there are a lot of GPS traces but they place the road some way off the aerial, I'd rather trust the average of traces than the aerial.
Do not try to recreate Google Maps or Map24 or whatever. Even without the legal problems, there is one thing to remember: we are better than them. This is very often true. I've seen it all: wrong street names, wrongly classified streets, streets that aren't there in reality (anymore). OSM is better than that. Or at least we try to be, and quite successfully so.
Map only, what is there, but if possible, map all that is there.
If you compare your mapping with eg. Google, you will find differences, and that is oh so very good.
Thoughts on the Bing aerials
First of all, this is so very helpful. Of course I know that they gain from the sheer workforce available at OSM, but it is foremost a gain for us. I'd like to predict that the gift of the aerials will lead to an increase of roads in the database higher than the TIGER import, and that by June 2011. I'd also predict that by then OSM will be the most complete collection of map data in one place.
But the imagery does have drawbacks: we don't know how old the pictures are. A good example is just around my corner. some ten years ago a touristic road had been moved to solve problems at a level crossing. Googles aerials are from the very start of construction, thereby still showing the old traffic flow. Googles maps show the old road. In the OSM database the new road exists correctly. The Bing aerials still show the new road in construction, which might be 7 years ago, and the old road still intact. So, an unsuspecting mapper might think the current version is wrong and correct that. In other words: when tracing Bing imagery in areas you don't know, inspect existing roads before editing them. If in doubt, don't touch 'em. And especially: do not remove any roads that seemingly don't exist, just because they don't show up on the aerials.
Some experiences of mine...:
2009-11-28 Some farmer got paranoid
I was driving around some quite white spaces around Much when I spotted an official streetsign pointing me up a hill. So, I guessed this wasn't on the map and I went there. After some 300 meters or so it became clear that the road leads nowhere, especially as a farm house was in the way. I turned in their yard as I didn't want to go back the whole way in reverse. When I was almost done turning, the farmer, who apparently owned the land, jumped into his SUV and fired it and its brights up. As I was on my way I didn't think much about that. Leaving his yard, I turned right along another way, the car kept following me with its xenon brights on. Great, can't see half of the way ahead of me. Shortly after that I faced a barn, this car still behind me, and no really good place to turn around in sight. So, I stopped and tried to turn on this narrow road. Well, I managed to turn and this farmer yelled at me: "Can you tell me, what you are doing here?" I thought: sure, but I won't. "This is private property!" he yelled. Well, wrong voice for me. "So? I could not see that! No sign except for the official road sign!" I yelled back. "You have nothing to do here!" he yelled, my reply: "Yeah, you might think so!" and I drove on, back to the very apparently public road. He followed me, but I was faster in a Nissan Micra shopping cart and went to a side road in the next village, he drove on and I followed him. He turned, I still followed him. He went pass his farm, I still followed. he turned, I followed. I don't really know why, but he behaved like such an asshole that I had to retaliate. I finally stayed at the entrance to his precioous farm area with lights and engine off. He returned after half an hour, I think he was still searching for me. Well, there is no sign that that was private proverty, no gate, no signpost, no nothing, so what was his problem? I small board of wood saying "no entry, I'm afraid of people" would have done the trick... I guess, I'll have to return some day soon...
2009-11-26 Some drunks got angry
There I was driving around Neunkirchen, when I noticed a girl lying in somones driveway and a guy on top of her. I turned around and my passenger asked if everything was okay. "Push off, wanker!" the girl cried. We both thought she meant him, so I parked the car facing the problem, brights on. The guy took some time to understand that they weren't alone anymore. We both got out and this guy staggered towards me, then changing direction toward my passenger, all the time in a fighting (*laugh* he was SOOO drunk) stance. The scene looked really menacing to the girl. We both thought she was drunk and about to get a really unpleasant encounter with a male. Okay, they were both absolutely beyond anything that should be acceptable. Well.. we moved in and the girl grabbed this guy and dragged him away (darn, he looked like somebody who could really need some beating up), as she realized that this really wasn't the place to play out pubertal games. They finally moved along. But although I am not a really conservative person, I still think it's wrong to try to get your wiener polished in somebody else's driveway.