Read contour maps with Book Isle: separate rise from horizontal distance

Closely spaced contours do not automatically have larger elevation differences. With fixed contour interval and scale, a shorter horizontal distance for the same rise gives a larger average slope. Read lawful terrain material in Book Isle and record legend, units and two invented segments separately. The app displays documents and stores reading records; do not assume automatic distance measurement, geospatial interpretation or route-safety judgement. This is map-reading arithmetic, not navigation from a practice map.

Record map edition and legend location

Open a lawful map or illustrated text and record map name, edition, chapter/figure and separate return locations for map and legend. Printed and file pages may differ, while reflowable pages change with type size; retain caption and nearby phrase. Identify contours rather than roads, boundaries or depth lines from the legend, not colour alone. Use a clearer original or mark unreadable labels unresolved rather than inventing elevation from a hill shape. Bookmarks support return, not terrain interpretation. Manually record unextractable values and verify each against the original.

Define contour interval as adjacent elevation difference

The original exercise has adjacent ordinary contours at 100,110,120 metres, interval ten metres. First to third crosses two intervals, giving twenty metres, not three times ten. Record three lines, two intervals and twenty-metre rise separately. Real labelled index contours may span several ordinary lines, so consult the legend instead of assigning ten between every thick line. Keep supplementary-contour conventions separate. This simple example explicitly omits supplementary lines and elevation discontinuities to isolate interval counting.

Convert map length to horizontal distance

Assume scale 1:10000, so one map centimetre represents one hundred horizontal metres. Segment A runs from the 100-metre to 120-metre contour over two map centimetres along a chosen straight transect, hence two hundred metres; B spans the same rise over one centimetre, hence one hundred metres. Both rises are twenty; do not divide map centimetres directly into metres. Measure on paper or with a suitable external tool, not literal screen centimetres after app zoom. An embedded bar scale enlarges with the map and can be compared proportionally; a numerical scale on a resized image requires verified output size for precise measurement.

Calculate percent slope from rise over horizontal run

A’s average percent slope is 20/200×100%=10%; B’s is 20/100×100%=20%. Both numerator and denominator are metres, leaving a dimensionless ratio; percentages are not ten or twenty degrees. These are endpoint-average slopes along chosen directions, not the whole hill’s steepest gradient. Surface walking length is not horizontal run. Check centimetre conversion for 1000%, or a reused A denominator if both answers are ten percent. Retain rise, run and formula. Equal rise with unequal horizontal distance is the controlled comparison here.

Verify shared conditions prior to comparing spacing

Under this example’s shared scale and interval, B reaches the same rise over shorter run, so contours are denser along that direction and average slope is larger. Across maps compare scale, interval, units and direction first rather than judging screen density alone. Convert feet and metres consistently. A cropped map without legend leaves unknown conditions; do not borrow a nearby webpage’s scale. Display size and real distance are distinct. Zoom improves label reading without steepening terrain. Retain source identity and chosen segment locations in each comparison.

Separate labelled elevations from interpolation

Use contour labels for endpoints explicitly on the 100- or 120-metre lines. For between-line points without extra evidence, give only an appropriate rough range, not invented precision such as 113.27 metres. A closed loop does not establish a fixed summit height; check spot heights, depression symbols and further contours. Our endpoints deliberately lie on contours so interpolation error is not hidden in the calculation. For cliffs, bridges or special mapping cases consult the legend rather than imposing ordinary continuous-slope rules universally. Stop precise calculation and record missing information when evidence is inadequate.

Return to the legend for unit and direction errors

Keep separate fields for elevations, interval, map length, converted run and percent slope. Investigate discrepancies field by field rather than blaming zoom. Recount 100→110→120 if three lines became three intervals; revisit the ratio definition if twenty percent became twenty degrees. Retain measurement direction because runs vary with direction, and never combine A’s rise with B’s distance. Exit and reopen map and legend to verify figure and edition. If a bookmark returns only to the legend without identifying the measured segment, add that location rather than claiming reproducibility from a bookmark alone.

Explain different slopes for the same rise

Keep invented A/B calculations separate from real-source notes. Explain three lines/two intervals, both twenty-metre rises and how runs of two hundred/one hundred metres yield ten/twenty percent. Repair unit or counting fields if you merely recall B is steeper. Limit real-map conclusions by sheet, direction, resolution and estimation range, without travel-safety or geological judgements. Another reader should reproduce calculations from legend and measurement evidence, not automatic terrain analysis. No field survey or exhaustive geospatial-PDF interaction test occurred. Recheck a new sheet or viewing scale rather than copying old values.

Related tutorials and sources

Keep geographical reading notes in Book Isle: distinguish shared names, older names and mapped features; Follow worked examples in Book Isle: track symbols, units and substitutions.

Sources checked on 9 November 2026: the official Book Isle App Store listing and Apple Lookup show version 1.1.4, requiring iOS / iPadOS 15.6 or later. This workflow uses local reading, search, bookmarks and notes for manual checking. Readers record the samples and conclusions; automatic chart recognition, statistical testing or proof verification is not assumed. Confirm available controls against the installed version and file type. The exercise does not claim step-by-step device testing in this batch.

Map-reading basis: USGS’s US Topo symbol guide explains equal-elevation lines, contour interval and spacing. Elevations 100/110/120 metres, scale and A/B distances are invented practice values, not a real survey area.