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If I have, say, a printed map at the scale of 1:20000 and the legend says that it was mapped at a scale of 1:10000 does this simply mean, that the surveyors/cartographers made drafts & sketches or used aerial photographs at that scale or can there be some other meaning?

Also, if the metadata of vector data say that its scale/resolution is e.g. 1:5000, can it have any other meaning besides having been digitized from a source (aerial photograph, printed map) of that scale?

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See my comment below for specific context (general answers are still fine).

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    Can you show us the exact legend text relating to the scale, and a bit more information on your 1:20000 printed map? Where did you get it? If the legend says 1:10k, then why do you think it is 1:20k? I'm not saying it isn't so, just trying to get a bit more info so we can make a good answer.
    – BradHards
    Commented Apr 3, 2013 at 8:17
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    Can't get at the legend at the moment, besides its in Finnish :P. The map is at the scale of 1:20000 and the legend says so. But descriptive text in the legend says that the map is based on aerial photographs and field work and the mapping (does not specify what part) was partly done at the scale of 1:10000. Maybe it's a reduction from drafts? I do have some literature on the specific kind of map, and was more interested if there is such a general concept as mapping scale as opposed to map scale in (pre-digital) cartography.
    – Torsti
    Commented Apr 3, 2013 at 8:34

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I do know that the Canadian National Topographic Survey (NTS) maps were originally based on air photos flown post WWII in the 1950's. The NTS maps are 1:50 000, and most of the air photos are 1:10 000 or 1:20000. Because air photos do not have a consistent scale across the picture due to radial distortion, the photos are ortho corrected, and then ground truthed prior to being made into a map at 1:50 000 scale. So, I suspect, though I am not certain, that there was an implicit concept of mapping scale as the raw material was translated into a final map. I hope that this helps!

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  • That's what I'd suspect generally, but I finally found that map description that prompted the question and it was actually geological soil map - so I'm no longer certain that the more accurate scale refers to aerial photography (in this specific case). I only have the meta data and digitized soil information, haven't seen the printed original, which might give more clues.
    – Torsti
    Commented Apr 24, 2013 at 5:41
  • Just out of curiosity, do the NTS maps specify the kind of aerial photos used or is this background information you'd get from other sources? At least the Finnish National Land Survey maps only state the year of the aerial photos used in map making.
    – Torsti
    Commented Apr 24, 2013 at 5:47
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Specifically concerning the Finnish Basic Map 1:20000 I found the following (from Suomen peruskartoitus 1947-1975, p. 41):

A photomap prepared from aerial photographs is usually compiled to serve as a base for mapping at a scale of 1:10 000. The mapping is carried out at 1:10 000 using a quarter of the map sheet, 5km x 5km, as a working unit. [...] The Basic Map is fair drawn on transparent plastic at 1:10000 [...] The Basic Map is printed at 1:20000 scale, to which the drawings are photographically reduced.

The text also mentions that the scale of the original aerial photographs was either 1:17 500, 1:22 000 or 1:31 000.

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