04 =V20? +20? +(37.5Y +25? =53 cm. 
For graphical stereo-restitution at a scale of 1:2,500, from aerial 
photography at 1:10,000 — 1:12,500 of rural areas (cadastral details plus 
general topography), a production (pencil plot only) of 2.5—10 ha per 
instrument-hour may be expected, depending on the density of the plani- 
metric details to be plotted. Average production: 5 ha/hr, per stereo-model, 
consequently, some 40 instrument hours are required for the pencil plot only. 
If therefore, in a certain country, it is desired to map in this way about 
5000 square kilometres annually, then 35 stereo-instruments are required 
provided the work is carried out with £wo shifts per day on each instrument. 
1.4.3 Mixed Graphical and Numerical Stereo-Restitution 
In order to extract, at least for the cadastral boundaries, the highest 
possible accuracy from the aerial photographs ( 0,7 28 cm in our example 
of section 1.4.1.2 above), one could, simultaneously with the graphical 
plotting of the cadastral boundaries, record the model co-ordinates of the 
plotted boundary points. Productivity at the stereo-instrument will not be 
significantly lower than for graphical restitution, though, for easy reference, 
the recorded model co-ordinates should be coded at the instrument (e.g. with 
code numbers referring to the parcel numbers). 
For the numerical restitution, a device for automatic digital recording, 
and a calculator—preferably an electronic computer— is a necessity.In the case 
of cadastral boundaries formed chiefly of topographic features, the main 
product will be a long list of transformed co-ordinates. The procedure leads, 
of course, to a confrontation with problems of mass data-processing, inspec- 
tion, filing and administration. 
1.5 A Possible Procedure 
As mentioned in section 1.2, the purpose of a cadastral survey is, in 
the first place, to fix the boundaries of a property for the legal protection 
of ownership and other rights of the land, and in the second place to have a 
basis for taxation. 
With regard to the legal aspect, a real geometrical survey of these boun- 
daries would not be necessary if no changes in the boundaries were expected