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Is it perfectly acceptable to produce a map at a scale of 1:24,000 from a database that was digitized from a 1:100,000 scale source map?

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    What do you mean by "perfectly acceptable"? What were the cartographic conventions on the 1:100k map? – BradHards Nov 17 '15 at 7:03
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Not at all.

When you have some data that was digitized at 1:100,000, it excluded smaller features, which were smaller than the Minimum Mappable Area.

For example, suppose you are dealing with topographic data.At 1:100,000 you would exclude large streams and trees.These features are visible at 1:24,000, and should be included in such a map.

If you just print the same data at a higher scale, then you are missing out on data, which should be visible at that scale.

Secondly, the accuracy of the data is different at these scales. Generally, you cannot make lines smaller than 0.8 mm on a printed map. This means that at 1:100,000 scale, your features are within a about 80 meters of that location. at 1:24,000, the feature should be within 20 m of the location that you have marked. Hence if you just print out your data at 1:24,000 your map would say that you are accurate to 20 m, when you are actually not.

  • I really appreciate it. Makes sense. – Sue Smith Nov 17 '15 at 8:08
  • This presumes certain cartographic conventions, which are not in evidence from the question. Probably reasonable, but you could choose to build a 1:24k map with really rough or radically different conventions. For example, there is no reason why streams or trees would appear on some maps, irrespective of scale. – BradHards Nov 17 '15 at 8:16
  • @BradHards: While you are technically correct, these examples were used only for illustrating that smaller features would be missing in the 100K map. The features and conventions would vary on a case by case basis – Devdatta Tengshe Nov 17 '15 at 8:23
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    Sure, and I just used them as examples. On some maps it might be completely OK to scale the data e.g. its a map of a farm, and the farmer just wants a big map of paddocks / fields to write in what is planted or housed in that paddock. Not a common example, but I think it is more complicated ("it depends") than this answer makes out. – BradHards Nov 17 '15 at 10:21
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Don’t disagree with any comments. With GIS it’s more important to define minimum mappable unit ( and minimum width of linear features) than scale per se - as scale doesn’t have the fixed/precise meaning like it used to. It’s also important to define the precision of the line work - ie how close the line work boundaries are to actual feature (relative to image although should be relative to ground). This is partly (mainly?) a function of scale the data is captured at as, as the comment above says, you can normally get linework within 0.8 mm so if the data is captured at twice the scale the precision will be half that ( assuming you take same amount of care digitising).

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