414
July 2020
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
Ocean inland along the drainage divide of the Great Scarcies
and Mélikhouré (rivers) to an in-definite point in the interior.
Later deter-mined by field surveys, the last agreement fixing
the boundary was signed on 04 September 1913. In places, the
boundary measurements are described to the closest half-me-
ter. Reading between the lines, I’d guess that the boundary
commission surveyors had people literally looking over their
shoulders during that process!
When the federation of the eight territories constituting
French West Africa came into being in 1904, the
Annexe de
l’Institut Géographique National á Dakar
had the local re-
sponsibility for topographic mapping. Also known as the Ser-
vice
Géographique de l’Afrique Occidentale Française SGAOF
(Geographic Service of the French West Africa), topographic
mapping of Guinea has been largely at the scales of 1:200,000
and 1:500,000. This agency has performed a small amount of
mapping at the scales of 1:20,000, 1:50,000, and 1:100,000.
Topographic mapping of Guinea was in the past largely the
result of rapid ground surveys. After WWII, the French ad-
opted aerial photography controlled by astronomical points
(“Astro” stations) as the means of surveying and mapping at
scales of 1:50,000 and 1:200,000. These compilations were
also used for derivative mapping at smaller scales. There is
complete coverage of the country at 1:500,000 scale, and at
1:200,000 scale. The latter consists of sheets mainly based on
ground surveys. A small portion of Guinea has 1:50,000-scale
topographic sheets compiled, mostly by the French IGN
in the coastal west, and by a cooperative agreement with
the Japanese (JICA) for some sheets around Kankan and
Kérouané-Macenta.
The oldest coordinate system in Guinea that I have been
able to locate (with help) is the Conakry Datum of 1905 where
Φ
o
= 9° 30´ 58.997 N, Λ
o
= 13° 42´ 47.483˝ West of Green-
wich, ξ
o
= –4.50˝, η
o
= –0.02˝, and the ellipsoid of reference
is the Clarke 1880 (IGN) where
a
= 6,378,249.2 m and
1
/
f
= 293.4660208. Thanks go to both John W. Hager, retired from
NIMA, and to Russell Fox of the Ordnance Survey of the U.K.
The origin point is at the Public Works Building in Conakry,
and John W. Hager went on to say: “Reingold cites
Les Man-
uels Coloneaux
, “Cartographie Coloniale,” Paris, 1935 and
“Catalogue de Positions Géographiques,” Paris, 1923 give the
position to the nearest second.
Annales Hydrographiques
, 4e
Série, Tome 1, Année 1950, Paris 1951, p. 155 gives the above
but is listed as 3rd order. A position for the Railway Astro
Pillar is given as latitude = 9° 30´ 54.5 N and longitude = 13°
42´ 47.1˝ W, a difference in position of 138.6 meters. I would
assume that the astro pillar was not permanently marked.”
Some minor hydrographic surveys were performed by the
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CERTIFIEDMAPPING SCIENTIST LIDAR
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