I've exported the map region to jpg in 1:1000000, the resolution, shown to me was 2019 x 1866; area сoordinates was so: N 56.9583; E 40.3617; S 54.3107; W 35.2828 (it is the Moscow oblast) so my question is: what should be the DPI factor (in photoshop for example) to print that image in 1:1000000 ???? because DPI factor by default is 72 and printed picture doesn't match to the scale 1:1000000. The same problem appeared in archicad, when I made import of the drawing (I tried it with JPG and Pdf format)the scale was also wrong. I'm working in metric system and I thought the problem is in that? but I tried different convertation and nothing helped??

I tryed to describe my question in link below

http://help.openstreetmap.org/upfiles/scale_factor.jpg

asked 12 Apr '12, 23:24

sergpomelov's gravatar image

sergpomelov
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edited 15 Apr '12, 14:26


That's what I did:

  1. Get an image of a known distance, at a given scale (say: 100m at 1:5000)
  2. Get map size it should have: 100m / 5000 = 0.02m = 2cm
  3. Measure that distance in pixels of obtained image: 100px so far surprise!
  4. Calculate: 100px / 2cm = 50 px/cm. That's the resolution
  5. Want it in inches? 50px/cm * 2,54cm/in = 127px/in

As this measures are quite inaccurate, maybe you should try with different distances and map scales. I made it twice, and the second time I got 112.27 px/in, so I think it should go around 120dpi.

Note: dpi is "dots per inch", and, as screen 'dots' are pixels, I used dpi and pixels/inch as the same unit.

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answered 13 Apr '12, 16:03

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samel
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I'm not so small, dady ))) But thanks a lot, Now i'm doing that with latitudinal way' I tape direct nombers in zone coordinates (not N 56.9583, but 57 not S 54.3107, but 54 not... and so on) the distance of 1_o of meredian is approx 111 km and it is quite all right for me.. for now... but I think that OSM steel needs to improve some resolution and unit parametr in export menu (for not to spand a time for that)

(14 Apr '12, 01:41) sergpomelov
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answered 14 Apr '12, 21:35

sergpomelov's gravatar image

sergpomelov
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may be that coment is not for OSM system, but for supporting products... SO, using Maperitive (now I began to work with vector :) )I tried to export OSM data to illustrator and Inkscape at the same time )) so... for my great wondering, after export that data to dxf format I found that in Archicad they came with different size... after a fiew hours of interest I understood some primitive thing ! attention ! INKSCAPE EXPORT DATA IN 90 DPI AND ILLUSTRATOR EXPORT IT IN 72 DPI ! attention ! at the same time the resolution of my monitor is http://members.ping.de/~sven/dpi.html see next coment

(15 Apr '12, 11:42) sergpomelov

1366 X 768 with 15.6" diagonal... (100.45 PPI/points per inch/)thats why imported data was a bit bigger. So I scale it down to my real monitor size. In my case it was 381,56mm to 341,86 (that is the exported box size not the monitor / my monitor size is 34.54cm × 19.42cm //see link, in previous coment by the way I found it in Maperitives help///and I exported it from INKSCAPE /90 DPI//PPI for monitor///)

(15 Apr '12, 11:55) sergpomelov

And as for OSM... Actualy I wouldn`t ever do all that if I onley had real 100mm leng virtual line (exportable to PDF) in the left down corner, close to the scale line (also exportable). But now I know everything about map scaling. Thanks for your attention.

(15 Apr '12, 12:13) sergpomelov

From that wiki page you get these basic formulas:

resolution = 156543.034 meters/pixel * cos(latitude) / (2 ^ zoomlevel)

The resolution means how many meters per pixel you get.

scale = 1 : (dpi * 39.37 in/m * resolution)

The scale means, how many cm in reality is 1 cm on the paper (or on the screen).

So if you have a screen with 96 dpi, you get that one pixel is 1.1943 meters. And you get a scale of 1 : 4 231 which means that 1 cm on your screen is 42.3 m in reality.

If you have a printer which prints 300 dpi … (now do the calculations yourself).

I hope this helps you getting the right size of your image.

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answered 14 Feb '14, 12:00

erik's gravatar image

erik
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accept rate: 9%

-2

The exported image is using mercator projection. This projection does not preserve scale. The exported image is scale 1:1000000 if you export an area near the equator, but this becomes a bigger scale the longer north or south you get. When you are comparing this map with a map in a projection that preserves scale better like utm you will see that they do not match. You will also notice other differences in the projections.

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answered 13 Apr '12, 01:28

Gnonthgol's gravatar image

Gnonthgol ♦
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accept rate: 16%

1

I dont think that answers the question. The problem is that the export tab lets you specify a 1:X scale, but that number is meaningless without an associated DPI (since the export is in pixels, it doesn't make sense to say "map is 1/Xth the size of reality" if you do not know the physical size of your printed/displayed pixel). The export tab should either say what DPI is used, or allow to set the DPI.

Concerning projection deformations: 1) zoom in sufficiently 2) let the export tab adjust the scale from the latitude.

(13 Apr '12, 10:53) Vincent de P... ♦

M ) I see, but the scale is smaller??

(13 Apr '12, 11:11) sergpomelov

zoom distanse does not matter, picture details depends on a scale factor you tape... as I understand... (and you always have maximum limit of a scale factor) and by the way, small scale line in low left corner is correct I checked it

(13 Apr '12, 12:55) sergpomelov

made the way you toled me using latitude !!! greate !!! I think somehow OSM arrange that problem later ) thanks a lof for hi light decision (hard to find it sometimes)

(13 Apr '12, 14:22) sergpomelov
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question asked: 12 Apr '12, 23:24

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last updated: 14 Feb '14, 12:00

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