2. 
  
Field work. 
Guiding and determining scales for each sheet. 
Delimitation of visible boundaries in the mosaics. 
Formulation of control-sheets. 
3. Results. 
Field-research to confirm previous points. 
Locating national land. 
a) Unapropiated land. 
b) National land. 
c) Excess land. 
Delimitation of colonies. 
Delimitation of,concessions for cattle-raising. 
Report of the results. 
Elaboration of adjoining maps by municipalities. 
Verification of date in the public property Register. 
Concentration of results and utilization program. 
V. DIFFERENT STAGES OF THE WORKING PLAN 
A) PHOTOGRAMMETRIC PROJECTS 
1. Flight Plans and the carrying out of the photogrammetric flights. 
Taking into consideration all the limitations imposed by the territory of the Mexican 
Republic, on the carrying out of photogrammetric projects, a regional classification was 
established, which is also included on an enclosed map, where six zones are established 
according to their climatic and topographic differences. 
These zones were useful for the elaboration of flight plans so as to be able to obtain ma- 
ximum efficiency from the equipment. Fig. 7. 
Taking into account previous experience in work carried out by Compafiíía Mexicana Ae- 
rofoto, different bases were established for each of these zones, so as to make it possible 
for the airplanes to move in such a way as to be able to make the best use of the best 
atmospheric conditions for the taking of aerial photographs. 
The convenience of having moving equipment within the same zones was considered. A 
special effort was also made to move from zone to zone to concentrate the working po- 
tential in the most convenient areas. As a result of this planning, the number of frustrated 
missions was reduced, which lowered costs considerably. Another favourable circumstance 
and one which it is necessary to mention-was that the Department of Agrarian Affairs and 
Colonization was able to authorize projects to be carried out during the last months of 
year, which gave us an opportunity to use fully the most favourable four months, from 
the climatic point of view. 
On a map of the Mexican Republic which can be seen together with N? 7, the air bases 
and the corresponding fields of work are indicated. Compania Mexicana Aerofoto, S. A. 
allotted four planes for the carryin out of the work. 
2. Compilation of ground control. 
While the photographic flights were in progress, compilation of land control at our dis- 
posal was carried out and this consists of located geodesic chains, as shown in the co- 
rresponding figure. For this purpose, all the topographic work has been carried out by 
the different offices, for other purposes. was taken into account. We must acknowledge the 
contribution of the Military Cartographic Department of the National Defense Ministry, the 
geodesic chain of which was a great use to us. We used the amplified charts of this Office 
at the scale of 1:250,000. 
We also made use of surveys carried out by the Ministry of Hydraulic Resources, of the 
Mexican Petroleum Company, of the Directorate of Geography and Meteorology of the Mi- 
nistry of Agriculture and Animal Husbandry. 
The land-control thus obtained was analyzed, with a revision of the persistence of monu- 
ments and we identified these monuments in the aerial photographs, in order to carry out, 
later on, the corresponding radial triangulation. 
14 
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Divisic 
base: 
Zonas