OpenStreetMap
I started off with the intention of mapping a few walkways near Wallaceville Railway Station and things sort of developed from there. Once I had aligned the imagery to the railway line between Ward and Blenheim Street crossings, I found that several nearby streets did not align with road centrelines, although others in the same area did align. Have made several small adjustments to various features, often moving road centrelines less than a road width (perhaps 3 or 4 metres) to line things up with road markings. And it just went on from there, as I saw more and more little discrepancies, incorrect and incomplete information. and missing parking areas, building outlines and other features. I can see myself taking a good walk around town with a new set of mapping eyes on and taking note of what I see.
Discussion
Comment from Warin61 on 2 June 2015 at 22:57
“Discrepancies”
of upto 10 meters can be had from a single GPS track .. and consider someone driving a car with a GPS and putting that trace into OSM.
in satellite imagery can be had due to elevation changes and a non normal view (not 90 degrees to the surface).
Does it matter? Well .. to the perfectionist yes … we all like accuracy. But as a user of the map .. you simply want a representation of what is there, some distortion is ok as long as the features are recognizable. Some paper maps deliberately distort the scale so they can better show details in certain places. So .. it matters .. a little. Don’t get to take with accuracy, better to get the more things of use on the map. If there is something you use/like that is not on the map that (to me) is far more important than getting things dimensionally ‘accurate’.
Comment from NZGraham on 3 June 2015 at 05:10
“If there is something you use/like that is not on the map that (to me) is far more important than getting things dimensionally ‘accurate’.”
I agree so much. Add ‘missing’ features first then follow up with enhancing accuracy.
Comment from Huttite on 3 June 2015 at 14:46
I understand and accept that a map may visualise features in a different way that reality. For example: The road width on a street map needs to be large enough to print the street name inside it, although this means it might seem to cover the front lawn and half the house on properties on both sides of a street. However, it is good to know that when putting something new on the map that if I have plotted it 5 or 10 metres away from its real world position, but, relative to everything else, it is in the “correct” position, then it is reasonably “accurate” even thought the position is not “precise”. And since GPS be unable to do much better, I can feel comfortable that my contributions are, at least, not harmful.