THE MAPPING OF HONG KONG
133
did not exist, with contours at 5 ft. vertical intervals (or spot-heights on flat reclaimed land) and adding contours to the detail sheets already surveyed by ground methods, and
(1) mapping all of the New Territories* not already mapped (including the islands) below the 600 ft. contour, at a scale of 100 ft. to 1 inch with contours at 10 ft. intervals and adding contours to the detail sheets already completed by ground survey.
This involved a total of:
(1) 364 new sheets (detail and contours) at 1/600 scale (50 ft. to 1 inch) and adding contours to 173 more at that scale, and
(2) about 730 new sheets (detail and contours) at 1/1200 scale (100 ft. to 1 inch) and adding contours to 347 more at that scale.
The air photography, taken at altitudes of between 2700 and 4000 feet, depending on the terrain and the scale of mapping, was completed by early February 1963. The next stage was the fixing of control points (co-ordinated on the Colony grid and with accurate levels) to form a framework on which the plans would be plotted.
The supply of the control point data, and the precise identification of each point on the photographs was the responsibility of the Survey Branch. This work was completed in early 1968, by which time a total of some 1,550 control points had been fixed.
The photogrammetric plotting was carried out in the contractor's offices at Boreham Wood in England and the first "machine-plots" were forwarded by air freight to Hong Kong in July 1963. Each sheet had to be checked on the ground and any detail which could not be clearly seen and identified on the photographs had to be surveyed by surveyors from the Survey Branch. In areas where there were many trees a considerable amount of important detail was obscured from the air and on some sheets several weeks' field work was required.
* Excluding a strip near the Sino-British frontier where air photography was not permitted.
THE MAPPING OF HONG KONG
133
did not exist, with contours at 5 ft. vertical intervals (or spot-heights on flat reclaimed land) and adding contours to the detail sheets already surveyed by ground methods. and
(2) mapping all of the New Territories* not already mapped (including the islands) below the 600 ft, contour, at a scale of 100 ft. to 1 inch with contours at 10 ft. intervals and adding contours to the detail sheets already completed by ground survey.
This involved a total of:
(1) 364 new sheets (detail and contours) at 1/600 scale (50 ft, to 1 inch) and adding contours to 173 more at that scale, and
(2) about 730 new sheets (detail and contours) at 1/1200 scale (100 ft. to 1 inch) and adding contours to 347 more at that scale.
The air photography, taken at altitudes of between 2700 and 4000 feet, depending on the terrain and the scale of mapping, was completed by early February 1963. The next stage was the fixing of control points (co-ordinated on the Colony grid and with ac- curate levels) to form a framework on which the plans would be plotted.
The supply of the control point data, and the precise identi- fication of each point on the photographs was the responsibility of the Survey Branch. This work was completed in early 1968, by which time a total of some 1,550 control points had been fixed.
The photogrammetric plotting was carried out in the con- tractor's offices at Boreham Wood in England and the first "machine-plots" were forwarded by air freight to Hong Kong in July 1963. Each sheet had to be checked on the ground and any detail which could not be clearly seen and identified on the photographs had to be surveyed by surveyors from the Survey Branch. In areas where there were many trees a considerable amount of important detail was obscured from the air and on some sheets several weeks' field work was required.
* Excluding a strip near the Sino-British frontier where air photography was not permitted.
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