Pet peeve time, folks. And it’s one that been getting my goat for years. Maybe it’s my vocation; perhaps I’m too closely tied to the issue to observe it objectively. It’s something, however, I encounter far too often: the inability to determine what constitutes a large-scale map and what constitutes a small-scale map. Here’s a brief gloss-over:
The map of Nakusp (1:20 000) on the left is a large-scale map in relation to the small-scale map of southern British Columbia (1:5 000 000) on the right. Scale ratios are representative fractions. When you see a ratio of 1:20 000, it means that the objects portrayed on the map are drawn at 1/20 000 their actual size. 1/20 000 is a larger fraction than 1/5 000 000, and thus the 1:20 000 map is of a larger scale. One can see how it could be considered somewhat counterintuitive: when you see a large number on a map in the millions, and the area covered by the map is large, you may lean toward that map as being ‘large-scale’ (our brains tend to associate ‘big’ with other things that are ‘big’). But this is incorrect. Those fractions are referring to the size of the object.
Large-scale maps are able to show more detail, since they can ‘zoom in’ on the features being displayed. Smaller-scale maps are more useful for giving broad overviews of large area. As a general rule, large-scale maps are considered to be anything greater than 1: 70 000; medium-scale maps are those between 1:70 000 and 1:400 000; small-scale maps are those beyond 1:400 000 (for example, pretty much anything you’ll find on a world atlas plate; anything beyond 1:1 000 000 is very small).
Compass Dude (n.d.). Map Scale. In ‘Map Reading’, Compass Dude. Available at http://www.compassdude.com/map-scales.shtml. Accessed 23 November 2010.
Davidson, R. (2002). 5-1. Representative Fraction. In ‘Scale and Distance’, Reading Topographic Maps. Available at http://www.map-reading.com/ch5-1.php. Accessed 23 November 2010.
Macquarie University School of Earth Sciences (n.d.). Large scale and small scale. Map Reading Skills Home Page. Available at http://www.eps.mq.edu.au/courses/GEOS264/maps/maphome.htm. Accessed 23 November 2010.
Rosenberg, M. (n.d.). Map Scale – Measuring Distance on a Map. About.com: Geography. Available at http://geography.about.com/cs/maps/a/mapscale.htm. Accessed 23 November 2010.
Wheate, R. (2010). Map Basics. Cartography and Geomatics 205, University of Northern British Columbia. Available at http://www.gis.unbc.ca/courses/geog205/lectures/powerpoint/mapbasics2.ppt. Accessed 23 November 2010.