Interpretation of Photographs
Senior 6 · Geography
Interpretation of Photographs
Lesson 1 of 4
22 min
In S2 you learned to name the three main kinds of photograph and to divide one into nine parts. At A level those skills become tools. A planner who wants the area of a farm needs a photograph that behaves like a map; a geographer describing the shape of a hillside needs one taken from the side. This lesson explains how the position of the camera controls what a photograph can show, how to find the scale of a vertical photograph, and how to say exactly where on a photograph something is.
Definition
Ground photograph (also called a horizontal or terrestrial photograph): a photograph taken from the ground with the camera held roughly level. Example: a photograph of a tea estate taken while standing on its access path.
Aerial photograph: a photograph taken from an aircraft, a drone or a balloon. It is oblique if the camera is tilted, and vertical if the camera points straight down.
Definition
Low oblique photograph: an aerial photograph taken with the camera tilted steeply downwards, so that the horizon is not shown. High oblique photograph: an aerial photograph taken with the camera tilted only a little, so that the horizon and some sky are shown.
Satellite image: a picture of the Earth recorded from a satellite. It is nearly vertical and usually covers a far larger area than an aerial photograph; many are made from recorded light that the eye cannot see, such as infrared.
Figure 1: the camera positions for the four kinds of photograph. The blue wedge is the part of the scene that the camera records.
| Type | Horizon and sky | What you see of objects | Scale | Good for |
|---|---|---|---|---|
| Ground | Usually shown | Their sides; near objects hide those behind | Changes greatly from front to back | Slopes, buildings, vegetation, people at work |
| Low oblique | Not shown | Tops and sides | Changes from front to back | A settlement or a landform seen in relief |
| High oblique | Shown | Tops and sides; a very wide area | Changes strongly from front to back | The general setting of a large area |
| Vertical | Not shown | Tops only (roofs, tree crowns) | Nearly the same everywhere on flat ground | Measuring distances and areas; making maps |
Worked example 1: naming the type, with evidence
Problem. Identify the type of each of the three photographs above and give two pieces of evidence for each.
Solution.
| Photograph | Type | Evidence |
|---|---|---|
| Tea estate | Ground (general view) | The tea bushes and path are seen from the side at eye level; the sky and distant mountains are visible; the near bushes hide the land behind them. |
| Kigali Convention Centre | High oblique aerial | Roofs and car parks are seen from above but at an angle, so the sides of buildings also show; hills and the horizon appear at the top. |
| Valabu farmland | Vertical aerial | No horizon or sky; only the tops of the fields and banks are seen; the field shapes look like a map. |
Ground and oblique photographs have no single scale: the same object looks smaller the further it is from the camera. A vertical photograph of flat ground, however, has almost the same scale everywhere, so it can be measured like a map. Its scale depends on the camera's focal length (the distance from the lens to the film or sensor) and the flying height of the camera above the ground:
Both must be in the same units. If the flying height is not known, compare a distance measured on the photograph with the same distance known on the ground (from a map, for example).
Worked example 2: scale from the camera
Problem. A survey aircraft flies at 4,600 m above sea level over farmland at 1,560 m, using a camera of focal length 152 mm. Find the scale of the photographs, and the ground length of a road that measures 4.5 cm on one of them.
Solution.
Note the step that is easy to forget: the flying height is measured from the ground, not from sea level. Using 4,600 m would give about 1:30 000, and every distance worked out from it would be about 50% too long.
Worked example 3: scale from a known distance
Problem. A straight road known from a map to be 800 m long measures 4.0 cm on a vertical photograph. Find the scale.
Solution. 800 m = 80 000 cm, so
Warning
Tall objects lean on vertical photographs. A tall building near the edge of a vertical photograph appears to lean outwards, away from the centre, because the camera sees its top and one side. The effect, called relief displacement, grows with the height of the object and its distance from the centre of the photograph. It also means the scale is larger on a hilltop (nearer the camera) than in a valley. Measure distances on flat ground near the centre when you can.
On a ground or oblique photograph, divide the picture into thirds in both directions, as you did in S2: foreground, middle ground and background from bottom to top, and left, centre and right from side to side. Combine them: "a domed building in the centre, on the line between the middle ground and the background". A vertical photograph has no foreground or background, since every part is the same distance from the camera. Describe positions on it as top, centre and bottom, and left, centre and right; if a north arrow is given, use compass directions ("in the north-east of the photograph").
Worked example 4: locating features on the Kigali Convention Centre photograph
| Feature | Section |
|---|---|
| Tree-lined car park | Centre and right foreground, and the right middle ground |
| Curved building with a patterned front | Left middle ground |
| Domed building (the convention centre) | Centre, on the line between the middle ground and the background |
| Multi-storey buildings | Left and right background |
| Hills on the skyline | Background, across the whole width |
When a large feature spans two sections, name both, or say which part lies where.
Tip
Exam technique. "Identify the type of photograph" is worth one mark for the type and one for each piece of evidence. Evidence is something you can point to on the photograph (the horizon, the sides of buildings, only roof tops), not a definition learned by heart.
ExamRevision: "Aerial Photographs – Types & Location on Photographs". An Irish revision video on the kinds of aerial photograph and on how to give the location of a feature on one. Compare its method for locating features with the one in this lesson.
Practice
Summary
Sources and credits
The text, Figure 1, the worked examples and the exercises were written and drawn by Ganzaa.
Video: "Aerial Photographs – Types & Location on Photographs", ExamRevision, embedded from YouTube.
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
