Appendix 1 - Surveying and mapping of large planting sites

Figure

Basic forest surveying and mapping is needed for efficient planning and management in reforestation. Information on the area is gathered and a sketch drawn in the field. The final map is completed in the office.

1. Recording of field data and drawing of field sketch

To collect and record the field data, a box compass is needed and sheets for field notes should be prepared. Try to get hold of maps and aerial photographs of the area, on as large a scale as possible. This will make the work easier.

The field work can be divided into three main areas:

(a) General orientation.
(b) Gathering of field data.
(c) Drawing the field sketch.

(a) General orientation

First, acquire a general knowledge of the area. Consult maps, note key points such as forest zone corners, rivers, roads or trails. Familiarize yourself with the terrain by walking around it and get an overview of the variation in site conditions.

Surveying and mapping

General orientation

1. Consult map

2 Walk around

Gathering field data

Compass

Aiming

Drawing the map

Protractor

Drawing

(b) Gathering field data

When you have a general overview of the area, start gathering the field data. Choose a starting point (point 1) that is easy to relocate and describe. Note it on the sheet.

Example: Point 1 - Corner road and plantation, big Acacia tree, 60 cm in diameter.

Now you have to use the compass. A second point (point 2) along the side you want to measure has to be chosen. Always choose a clear landmark to point the compass at - for example, a characteristically shaped tree or a rock.

Occupy point 1, facing the direction of point 2. Hold the compass steady in both hands with your elbows against your body. Then sight point 2 by pointing the front sight of the compass to the landmark chosen as point 2. When the needle stops swinging, read the bearing to the nearest degree. Record the compass reading in the column provided in the field note sheet in line with point 1-2.

When using the compass, make sure that it is free from the effects of magnetism due to iron objects carried by yourself or in nearby surroundings. Otherwise you will get false readings.

Measuring the distances between the points can be done by pacing. The number of paces for 100 metres has to be known so that you later can convert the number of paces recorded into metres. The pace length is individual and must be measured for each person. For exact maps, a tape chain or a rope with metre graduations can be used for measuring. Note on the sheet the number of steps taken to cover the distance. Describe easily defined points and corners in the field note under the column "note". For example: Stone 1 x 2 m, 1 m high, east bank of river.

Survey field notes - suggested outline

(c) Drawing the field sketch

At the same time as you collect the compass bearings, trace a field sketch. Orient the sketch so that the top of the map indicates the North.

In the field sketch, mark the starting point as point 1. Mark point 2 and draw the line between point 1 and point 2. This is just a field sketch and there is no need to be exact but try to use a convenient scale (do not make the sketch too small) and to make the line more or less follow the direction in which you are going (the compass bearing). Then indicate the details of the area traversed.

As you proceed to the next station, take note of and indicate carefully the vegetation cover and natural land marks you come across. If you come across roads, trails streams, take a compass bearing of their direction. Mark them in the sketch with arrows.

Show the approximate extent of different vegetation covers by drawing light lines. Use a square on the sketch to indicate corner points.

Large areas may be divided into numbered compartments of 10-20 ha, and sub-compartments of 1-3 ha, to facilitate orientation, planning and management.

It is preferable to subdivide areas according to natural features (rivers, ridges), existing roads or tacks, and distinctively different ground cover (rocky areas, swamps, rich vegetation, poor vegetation).

Figure

2. Tracing the final sketch

Now the rough field sketch should be turned into a more exact final sketch using all the information collected.

(a) Decide the scale of the map.
(b) Plot the map.
(c) Correction of the sketch.
(d) Determining the area.
(e) Add the details.

(a) Decide the scale of the map

To produce a map of a convenient size, the actual measurements on the ground have to be reduced to a certain scale. According to the scale chosen, the map is a projection in proportion to the reality.

The scales most commonly used in forestry are 1:5,000, 1:10,000 and 1:20,000.

If the scale used is 1:5,000, 1 cm on the map represents 50 m on the ground and 100 m on the ground represent 2 cm on the map. If the scale used is 1:20,000 then 1 cm on the map represents 200 metres on the ground and 100 metres on the ground represent 0.5 cm on the map. The smaller the scale, the bigger the resulting map of a certain ground measurement.

Select an appropriate scale so that when plotted, the map is well contained on the sheet and the details can be clearly seen.

(b) Plot the map

Use graph paper. Always consider the top of the plotting paper as North. In the upper right hand corner of the sheet, place an arrow pointing north and the scale adopted for the map.

Examine the field notes and the field sketch to determine the length and the general direction of the surveyed area. Thereafter decide where on the sheet you should start so that the sketch is placed more or less at the centre.

To transfer the bearings measured with the compass onto the sheet, a protractor is eded. There are two kinds of compasses. One divides the circle into 360 degrees, the her into 400 degrees. Be sure that the protractor has the same number of degrees as the compass used.

Mark point 1 with a dot on the plotting paper and place the protractor so that point p coincides with the dot.

Then mark the reading or bearing by a light dot called a "guide dot". Place a ruler with the "0" graduation of the scale over point 1, and its edge touching the guide dot. Plot the distance between point 1 and 2 according to scale adopted.

The procedure is repeated until all the stations of the survey are plotted. Indicate the corner stations by enclosing them with squares.

(c) Correction of the sketch

When plotted, the final line seldom closes the area completely, because of errors in taking the bearings and measuring distances. When correcting this, point 1, the starting point, remains fixed, and the other corner stations have to be adjusted.

One method of deciding on the adjustment is to draw a straight, horizontal line AB. The length of this line should equal the total length of the measured sides of the area. Use the same scale as used when plotting the map - e.g. 1:20,000. On this line, mark off corner stations from point A at intervals equal to their respective plotted distances. At point B draw a perpendicular line equal in length to the gap between the first and last station when plotted "y". This line is called BC. Then draw the line AC. Erect lines from every point (each indicate one corner station) to line AC. These lines determine the distances by which the stations will have to be moved in order to close up the area.

The broken line figure at the foot of the opposite page is the first sketch plotted. Draw from the corner stations, light lines parallel to line "y". Along these parallel lines the stations are moved downwards, and the distance is determined for each point above (the distances between AC). The adjusted stations in the figure are connected by a solid line which now represents the area surveyed.

In this example the stations had to be moved downwards. If the last station on the sketch ends up below the starting point they will have to be moved upwards.

Figure

(d) Determining the area

The sketch is drawn on graph paper, which is divided off into squares. To determine the area, count the number of squares representing the plantation inside the area. The portion of divided squares is estimated and added to the area of whole squares. If the scale is 1:5,000 and the size of the squares is 0.5cm by 0.5cm, one square equals 625 square meters (25x25 meters). Sixteen squares would make one hectare.

(e) Add the details

Transfer all important details from the field sketch to the final sketch. Show the different vegetation covers by light lines. Indicate them by using abbreviations or with different coloured pencils.

Explain all signs and colours used to avoid misinterpretation.

Final map