19
ba
bo
Cadastral Survey in Urban Areas
In principle, all the items discussed in section 1 above apply.
2.3 General Purpose Large Scale Maps covering the Urban Area
In order to carry out efficiently the services expected of them, tech-
nical and administrative departments of a municipality need large scale maps
which cover the entire urban area. These maps have to satisfy the following
purposes.
I They must provide a general inventory of the many man-made objects
together with all other topographical details.
I They must assist in the management of public properties.
HI They must serve the planning of the city development.
Although for these purposes a very large map scale may be required
(e.g. 1:1,000—1:2,000) because of the very high density of objects per unit
of surface area on the ground, this does not mean that very great accuracy
is necessary. Great accuracy may be required when constructional works
have to be carried out (widening of streets, renovation of city quarters,
construction of subways, etc), but this usually involves limited areas only.
The procedure selected for city-wide urban mapping should not necessarily
be based on the accuracy required for such purposes. Instead it is often
preferable (i.e. more economical) to meet these special purposes with a
special solution.
For conventional graphical stereo-restitution of a city quarter at a scale
of 1:1,000, for instance, the photogrammetric production of a precision
plotter is often as low as 0.5 ha per hour for the pencil plot only. If one
employs, to this end, a negative scale of 1:5,000, the plot of one stereo-model
would take about 80 hours !
2.3.1 Photo Mapping
The productivity of 1:1,000 line mapping mentioned here may be too
slow to satisfy the urgent needs of the city planners. A good example of these
is given in a paper presented to the 2nd National Conference on Urban
Surveying and Mapping in Canada, in 1972. The paper was presented by the
Chief of the Surveys Section of the City of Ottawa, W.J. MacLean. It is
