ON SURVEYING AND MAPPING

Measurement & Scale

Measuring areas –

Planimeters

Measuring Gradients –

Gradient = Vertical height Difference / Liner Distance

Reading information on maps and diagrams

Symbols grouped into:
1. location phenomenon
2. quantitative distribution

Dot maps – distribution of dots
Dot diagrams
Scatter Diagram
Symbols – circular and rectangular
Flow lines – varying width according to values they represent
Diagrams using circles & rectangles

Representing quantity by isometric lines – lines joining equal measurement or value
Contour lines – same height
Isobar – same barometric pressure
Isohyet – equal rainfall

Chloropleth maps – maps depicting shaded areas of statistical or administrative
Convenience
Line Graphs

Principles of Linear surveying (Practical)

Linear Measurements

A steel or invar tape, 10 arrows
2 persons needed
Leader (L), Follower (F)

Leader moves away from follower, Aligned by arms, when aligned hands up

Linear measurements by single surveyor

By foot
By cycle wheel & counter
Distance = number in counter X cycle radius

Overcoming obstacle in linear measurement

Connecting measurements to their horizontal equivalent

Map – linear distance
Surveying – might be up or down slope
HE = M cos D

HE = Horizontal Equivalent
M = measured distance
D = angle of slope

Angular measurements

In Vertical Sense: Clinometer
Abney level
Watkin Clinometer

Measuring Height & difference in Elevation

Reachable base: b=a tan 0
Unreachable base: b = a / (cot 0 – cot o)

Simple measurement with a 45 set square

The setsquare is held upright in the palm of the hand with the short side horizontal & long side vertical. The observer walks backwards until the object is exactly in line with the long side of the set square.

Measuring Horizontal angles

Prismatic compass

Fieldwork in geography (Important)

Mapping land use

Example classification
Forest and woodland
High forest – big trees with crown touching
Coppice – woodland cut over for fencing
Scrub – small bushes or tress unfit for cutting
Forest cut down and not planted
Meadowland & permanent Grass
Arable (Including rotation grass & fallowland)
Heathland, moorland, Commons, rough hill pasture including swamps
and marshes
Gardens, Allotments, Orchards, Nurseries
Unproductive land
Buildings, yards, mines, cemeteries, wasteland
Ponds, lakes, Reservoirs

Preparing for field work

· definitive study of one small area
· scheme of classification of the area
· system of mapping to be adopted

Maps and their interpretation

Map projections:

Cylindrical projection – correct at the equator
Conical projection
Azimuthal projection – correct at polar

Some commonly projections:

Mercators
Galls
Conical with one or two standard parallels
Bonne’s
Samson – Flamstead sinusoidal
Mollweide’s
Lamberts’ Zenithal equidistant
Zenithal equal Area

Small scale map – atlas type
Large scale map – topographical type

Physiographical analysis of topographical maps:

Physiography – Area’s degree of roughness
How steep and how long slopes are
The depth of Valleys
What proportion of the land lies in different elevations etc
How hills and valleys are arranged

Topographic maps: shows shape of earth by contour lines

Techniques of studying topographic maps

Those which are based directly on the contour map
Turning the contour map into one aspect of physiography instead of elevation
Frequency curve: total amount of land lying above different elevation expressed as percentage of total area

SOURCE

PRACTICAL WORK IN GEOGRAPHY
B.J.GARNIER