Plans of an area, azimuth and contour lines

At an orienteering race near Gabala, Murad is handed a card: “From the spring, walk 400 m on an azimuth of 60°, then go round the hill along the 150 m contour line.” A runner with a compass and a plan finishes in minutes; one without them gets lost in the forest. In this lesson you will learn how the ground is drawn on paper and how to read directions, distances and relief on a plan.

The plan of an area and map symbols

Plans, maps and globes are compared in the lesson “Maps and scale”; here we learn the “language” of a plan. A plan uses four kinds of symbols:

• Scale (area) symbols — objects whose area is drawn to scale: a forest, an orchard, a lake, a field. You can measure their outline on the plan and work out the area.
• Non-scale (point) symbols — objects too small to draw to scale: a well, a spring, a single tree, a windmill. The plan shows where they are, not how big they are.
• Linear symbols — objects whose length is to scale but whose width is not: a road, a river, a fence, a power line.
• Explanatory symbols — give extra information: the direction of a river’s flow (an arrow), the kind of trees in a forest, the length of a bridge, the depth of a well.

Drawing a plan in the field is called surveying. At school we make a sketch (eye) survey: directions are measured with a compass and distances in steps. In the polar method the observer stands at one point and measures the azimuth and distance to every object; in the route method the observer walks along a path and records the azimuth and the distance at every turn.

1. 1
   Measure your step

   Pace a 10 m distance several times and find your average step length (usually 0.6–0.75 m).

2. 2
   Choose a scale

   The whole route must fit on the sheet, e.g. 1 : 2000 (1 cm to 20 m).

3. 3
   Measure each leg

   Count your steps to the next turn and take the azimuth with the compass; convert the distance to metres, then to centimetres on the plan.

4. 4
   Draw and add symbols

   Draw the north arrow, draw each leg on its azimuth and add the objects along the way with symbols.

Directions and orientation

There are four main directions — north, south, east and west — and four intermediate ones: north-east, south-east, south-west and north-west. Working out your position relative to these directions is called orientation. There are four main ways to do it:

• With a compass: one end of the magnetic needle always points north. Hold the compass level and, when the needle settles, turn the dial so that 0° (N) is under its north end.
• By the Sun: north of the Tropic of Cancer, including Azerbaijan, the Sun is due south at local noon, and the shadows of upright objects point north.
• By the Pole Star: Polaris, in the Little Bear (Ursa Minor), always appears in the north. You find it on the line through the two end stars of the Big Dipper’s “bowl”, about five times their separation away.
• By local signs: snow melts sooner on south-facing slopes; moss and lichen usually grow on the north side of trees and rocks; anthills are usually built on the south side of a tree. These signs only help — always check several of them.

Azimuth and back azimuth

Contour lines, contour interval and isobaths

Absolute and relative height are explained in the lesson “Landforms: mountains and plains”. The most exact way to show relief on a plan or a topographic map is with contour lines. Imagine a hill being flooded by water that rises 10 m at a time: every “mark” the water leaves on the slope is a contour line. Seen from above, these marks look like closed curves lying one inside another.

• The closer the contour lines, the steeper the slope; where they are far apart, the slope is gentle.
• A short tick on a contour line — a slope tick (bergstrich) — points downhill: outwards on a hill, inwards in a hollow.
• Height labels on contour lines are written with their tops facing uphill.
• If heights increase towards the centre it is a hill; if they decrease it is a hollow. Contour lines never cross each other.

The relief profile: building and choosing it

A relief profile is a vertical cross-section of the ground along a chosen line A–B: it shows how steep the slopes are and where the tops and hollows lie. Drawing a profile is a graphic method of map analysis, and DİM usually asks you to pick the right profile out of five.

1. 1
   Draw the line A–B

   Join points A and B on the plan with a straight line.

2. 2
   Mark the crossings

   Lay a paper strip along A–B, mark every place where the line crosses a contour and write its height. Estimate the heights of A and B from the nearest contours too.

3. 3
   Draw the axes

   The horizontal axis is the length of A–B (at the plan’s scale). Mark heights on the vertical axis in steps of the contour interval; the vertical scale is made larger, otherwise the relief looks too flat.

4. 4
   Join the points

   From each crossing go up to its height and join the points with a smooth line. Between two neighbouring crossings of the same height the line bends either up (a hill) or down (a hollow).

5. 5
   Check

   Where the contours are crowded the profile must be steep; where they are sparse it must be gentle.