The
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.
FUNDAMENTAL
DATA
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
293.465
TOPOGRAPHIC
MAPPING
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.
…………………………………………
E.E.M
JENG
(LAND
SURVEYOR)
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