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- Showing height on maps, and reading aerial and satellite images
Showing height on maps, and reading aerial and satellite images
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A flat map has to show hills and valleys somehow. Contour lines, spot heights and photos from above help us picture the land.
Contour lines
Contour lines join places of the same height above sea level. On 1:50,000 OS maps they are usually drawn every 10 m.
Lines close together show a steep slope. Lines far apart show a gentle slope.
A spot height is a dot with a number showing the exact height. A trig point (a blue triangle) marks a surveyed height, often on a hilltop.
Lines close together show a steep slope. Lines far apart show a gentle slope.
A spot height is a dot with a number showing the exact height. A trig point (a blue triangle) marks a surveyed height, often on a hilltop.
Reading the shape of the land
Contours that make V shapes pointing uphill usually show a valley (often with a river).
Circles of contours getting higher towards the middle show a hill.
A cross-section is a side view of the land, drawn by marking where contours cross a straight line and plotting their heights.
Circles of contours getting higher towards the middle show a hill.
A cross-section is a side view of the land, drawn by marking where contours cross a straight line and plotting their heights.
Aerial and satellite images
Aerial photographs are taken from aircraft or drones. Vertical ones look straight down, like a map. Oblique ones are taken at an angle, so you see the sides of hills and buildings.
Satellite images cover huge areas and are taken again and again, so they show change, such as deforestation or a growing city.
Geographers compare photos with maps to identify land use.
Satellite images cover huge areas and are taken again and again, so they show change, such as deforestation or a growing city.
Geographers compare photos with maps to identify land use.
Contour lines on one side of a hill are very close together and on the other side far apart. Which side would be easier to walk up?
- Close contours mean the height changes quickly over a short distance: steep.
- Far-apart contours mean the height changes slowly: gentle.
- So the side with far-apart contours is easier to walk up.
Answer: The side where the contours are far apart, because the slope is gentler.
Contours join places of equal height; close together means steep, far apart means gentle. Spot heights and trig points give exact heights. Vertical aerial photos look straight down; oblique ones are angled. Satellite images show change over time.
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