Two contour lines on a topographic map can never cross one another because that would mean
Answer: A
A contour joins points of a single height, so an intersection would place two heights at the same position. The one apparent exception is an overhanging cliff, which is why such features are drawn with a special symbol instead.
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State whether the following is true or false.
Every contour line either closes on itself or runs off the edge of the map.
Answer: B
Correct answer: True
A contour is the locus of all points at one height, so it cannot simply stop: the ground at that height continues somewhere. Either the line returns to close on itself, as it does around a summit or a hollow, or it leaves the sheet and closes beyond the neat line. A contour that appears to end within the map is a drawing error, not a landform.
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Contours that are close together indicate
Answer: C
Close spacing means a large height change over a short ground distance, which is steepness. Widely spaced contours mean the same height change is spread over much more ground, so the slope there is gentle. Reading spacing as gradient is the first skill a map user acquires.
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Where a contour crosses a valley, the V it forms points
Answer: D
Correct answer: upstream, towards higher ground
The valley floor is lower than the ground on either side, so a contour following the hillside has to run further up the valley before it finds ground at its own height. The V therefore points upstream. It is the single most useful reading rule on a contour map, because it identifies both the drainage lines and the direction of flow without any water being drawn at all.
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State whether the following is true or false.
A contour crossing a spur forms a V pointing uphill, in the same way as a valley.
Answer: A
Correct answer: False
A spur is the opposite case and gives the opposite V. The ground on a spur is higher than that on either side, so the contour bulges outward and downhill, and the V points downhill - away from the high ground. Valley Vs point upstream, spur Vs point downslope, and telling the two apart is what lets a reader distinguish a ridge from a re-entrant.
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A closed contour drawn with short inward-pointing ticks represents
Answer: B
The hachures distinguish ground falling inwards from a plain closed contour, which would be read as a summit. Without them a crater and a hill would be drawn identically, since both are closed loops with the same height on the line.
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A saddle, or col, on a topographic map appears as
Answer: C
Correct answer: a low point between two summits
A col shows as an hourglass: contours closing around a summit on either side, with the pattern pinching in between them where the ground dips. It is the lowest point on the ridge joining the two summits and the highest point on the line crossing from one valley to the other, which is why passes and routes go through it.
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The vertical interval of a contour scheme is
Answer: D
Correct answer: the height difference between successive lines
The vertical interval is a height, fixed for the sheet - 10 m, 20 m, 50 m as the scale and the terrain require. The ground distance between two contours is the horizontal equivalent, and it varies from place to place as the slope varies. Confusing the two makes every gradient calculation wrong, since the gradient is the ratio of the one to the other.
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Two adjacent contours 20 m apart in height are separated by 400 m on the ground. What is the gradient?
Answer: A
Correct answer: 1 in 20
\[ \frac{20\ \mathrm{m\ rise}}{400\ \mathrm{m\ horizontal}} = \frac{1}{20}. \] Gradient is always the vertical divided by the horizontal, expressed as one in something, so the larger the number the gentler the slope. Writing it the other way up gives 20 in 1, an unclimbable cliff, which is offered here as a distractor.
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A hill rises from 240 m to 480 m. How many contour lines are crossed if the interval is 20 m?
Answer: B
Correct answer: 12
With a 20 m interval the contours between the two heights are those at 260, 280 and so on up to 480 - that is \[ \frac{480-240}{20} = 12 \] lines. The 240 m level is the starting point rather than a line crossed on the way up, which is why the count is 12 and not 13. Dividing 480 by 20 gives the 24 offered, and ignores where the climb began.
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