MAP READING / THE PRINT-SIZE TRAP
Print a map bigger.
The ratio changes.
A label saying 1:50,000 belongs to a particular map size. If you enlarge the page, measuring against the old ratio can give the wrong distance.
Try the free tool ↓A scale-arithmetic lesson for uniformly resized maps. Not navigation, survey, route planning or a model of historical map accuracy.
THE INTERACTIVE WORKSPACE
Correct the ratio before measuring
Same feature on the paper — relative lengths, not a ruler:
Original size
USE IT IN REAL LIFE
The geography stayed still. The paper changed.
A ratio scale compares the same units: at 1:50,000, one centimetre on the original map represents 50,000 centimetres, or 500 metres. USGS explains the ratio-scale convention.
At 150% print size, the same feature becomes 1.5 times as long on paper. Divide the original denominator by 1.5. For 3 cm on that enlarged copy, the example distance is 1 km, not 1.5 km.
A graphic scale bar enlarged along with the map can still be measured against the copy. A printed ratio label does not update itself. “Fit to page” may resize by an unknown amount: do not guess the percentage.
This calculation assumes uniform resizing and an appropriate local scale. A stretched image, projection distortion or an inaccurate historical map can break those assumptions. A straight-line distance also says nothing about actual routes or travel time.
What if I do not know the print percentage?
Compare a known feature length on the original and the copy, using the same units: copy length divided by original length, times 100. Without a trustworthy reference, this tool cannot recover the scale.
THE NEXT STEP
Make place part of the investigation.
PastRush combines history case files with maps, evidence and chronology. Explore where events happened, compare sources and follow explanations rather than memorising isolated dates.
Get PastRush on the App Store ↗Six investigations are free. The optional Founder Lifetime purchase adds cases 7–12 and more content, without a subscription. Satellite maps and some location features require internet. This scale tool is a separate companion.
Publisher disclosure: Honest Little Apps publishes PastRush and this companion. This is not an independent review. App details checked November 4, 2026.
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