Jun 18, 2015, 10:03 AM
survey department is the national organization responsible for all forms of
cartographic activity in the country. It was created in April, 1914 though its
establishment was mooted out much earlier by lieutenant Governor George Rendall
in the early part of the nineteen century as can be seen the following extract
dated 1836 to the secretary of state for colonies.
“ I hope your lordship will feel disposed to grant the civil establishment a surveyor of land as it becomes necessary that each individual should have his position of farm land marked out to him in order that there may be no dispute’’.
It was not until April, 1914 that a land officer and surveyor was appointed in the person of W.F. Crook.
In the years 1904 and 1905 an Anglo-French Boundary commission was appointed headed by Major E. L. Cowie Chief British Commissioner and Mr. A.B.B. Tscharner, Assistant British Commissioner from whose work the Gambia Map of scale 1/250,000 was reproduced. This is oldest Topo map of the Gambia in the department. Of course the settlement of Bathurst being the first town in the county to be developed in the modern sense was first surveyed by the colonial engineer, J. H. Brady in April, 1889. The ancient may of the Gambia as existed in the earlier centuries had been compiled by discoverers and travellers.
Amongst the function of the department are the following:-
(a) The establishment of Horizontal and Vertical control over the entire territory by traversing and leveling which could be used as the basis of all surveys including topographical mapping, road location, township and cadastral mapping, and engineering surveys,
(b) The production of cadastral plans for lease purposes.
(c) Continuous revision of all maps of the country.
(d) Valuation of property for administration and as security for public loans.
As the terrain of the country does not admit triangulation to establish horizontal control due to the absence of well-defined hills, ridges etc. first order traverses were considered to be the only means of providing adequate frameworks for the country.
In 1954 – 1957 the precise traverse was inaugurated using catering tapping with an invar tape standardized at the national physical laboratory, teddington, and tavistock theodolites reading to single second for the angular observations. azimuth observations at every 25 stations or ten miles were taken to check the bearing, thetraverses were made in loop and the first loop from Bathurst to Mansakonko via the south Bank of the River thence North to Farafenni and back to Bathurst via the North Bank of the River covering a distance of approximately 200 miles with a misclosure of the order of 1/100.000.heighting was trigon metrical method. The second loop from Mansakonko to Kuntaur via the south Bank road thence along the North Bank road to Farafenni concluded the work financed under the colonial development and welfare fund.
In 1967 under the United Kingdom and the Gambia Technical Assistance Agreement, The third loop was launched and this time electronic distance measuring equipment known as Tellurmeters are being employed to measure distance and wild theodolites which read to a second are being used for the angular observations. This loop which is still in progress will conclude the framework.
The second order leveling which follows the main trunk road and the secondary roads in the Kombo peninsula was commenced in 1960 and designed to follow the route for the precise traverses. it has now reached Illiassa from Bathurst via the south Bank crossing at Yellitenda to the North Bank. The accuracy amid at is +0.02/m where M is the miles; this work is still in progress.
The map projection adapted for the Gambia is the restricted Transverse Mercator projection (Senegal Belt) with its standard meridian 160 west of Greenwich meridian. the true origin it the intersection of latitude 1300 North and Longitude 160 west and the co-ordinate of false origin are northing 500,000 meters Easting 400,000 meter, centured scale factor = 0.99975. The Figure of the Earth used is Clarke 1880 spheroid.
Equatorial Semi axis A= 6, 378, 249, meter. Flattening F = 1
The quarter million map mentioned earlier is the only topo map of the Gambia surveyed and compiled by the traditional ground method .i.e by plane tabling. traversing by compass, theodolite and chain to survey the salient features, such as river and its tributaries, streams, outcrops, road and tracts, foot path and villages etc. the Gambia occupies an area of approximately 4,150 square miles and lies between latitudes 130.04 to 130. 40 north of Equator and longitude 130.48’ to 160. 49’ west of Greenwich meridian, it has more of length than breadth, in the extent approximately 300 miles west to east and average width of 16 miles North to South.
However, new maps of the Gambia are now drawn on the U.T.M and all co-ordinates transformed to this projection.
The mapping of Bathurst, the major river ports, large towns and important villages commenced in 1910 and in 1950 almost all were completed. Revision of some of the trading ports and other towns were carried out and are still continuing.
There is as yet no cadastral series covering the country. It is only public lands and some private properties that properly surveyed cadastrally for preparation of title of lease.
The basic maps of the Gambia were compiled from the R.A.F air photography of the country at 1;30,000 in 1946 – 1947. There are 30 sheets at 1:50,000 covering the entire territory. in 1956 a more popular map was compressed from this at a scaled of 1:125,000 in 3 sheets, and a re-photography of the middle part of the territory to enable a land use survey to be made was carried out thirty four fully coloured land use maps at 1: 250,000 were published in 1960.
In 1960 a large scale air photography of Bathurst and Fajara was obtained for engineering works connected with coastal defence of Bathurst area. The photography was ultimately used for 1:2,500 mapping of Bathurst, Fajara and Cape St. Mary.
Air photography was flown in 1964 under contract of some 900 sq. miles of the Kombo St. Mary and the Western Division so as to produce from it 1/25,000 contour maps of the Kombo peninsula and used to enable a land use to survey to be made of this western part of the country south of the river Gambia.