The lack of cartographic base for cartain regions, has taken to a more intensive use of aerial photographies of small format as a source of agile spatial information and of a low cost to the system users which treat georeferencing images to several purposes, specially to the Rural Municipal Technical Cadaster (RMTC), which demands that the magnitude of the errors inherentin the process be known. A study was developed in order to quantifi the inaccuracy, originated from the straight use, with no restitution of these aerial photographies in the two main ways of entrance of the spacial information in these systems: the manual digitizer, through digital table, using the CR-SIGDER 2.0 system, and the electronic digitizer, through scanner, with direct vector, in the screen SVGA, with mouse, using the CR-IMAREA 1.0 system. The supporting points to the transformation of scales were transformed to the UTM system through GPS and topography. The main parameter analysed was the average error of the position in the co-ordinates. There was also the attempt to discover which is the best distribution of the field supporting points to the scale transformation in these systems. The best point distribution presented a 6.96 meters average error of position in the coordinates to the digitizer table, and a 7.53 meters on to the SVGA monitor. Taken into account the small scale used, these results show the big potencial of aerial photographies of small format to the purposes proposed in this work, since they are translated in errors of distances and areas in the topographic tolerance, as long as the supporting points are distributed one in each corner of the aerial photography.
rural cadaster; aerial photographies; georeferencing
