CadastreGPS / Equipment

Municipal cadastre, which method is appropriate

Several years of surveying, and this question is always very common. What method is the best to register?

We admit that this is not a recipe, as there are different conditions that must be taken into account and each method can have opposite variables in different territories. So to give light to the post, let's chew on some aspects that may be useful for decisions, incidentally to rescue the productivity of a discussion forum started a couple of days ago.

Cadastral survey methods

Why municipal cadastre.  I clarify this, because the post is applicable to an environment, in which a municipality wants to do its cadastre, either by its own means or with the support of a cooperation project. It does not apply to a large modernization project at the regional or national level, led by a centralized entity, which will have better conditions to execute the project and more money to spend… but also more surplus indicators to meet.

The scenario is, therefore, a municipality, of regular size, that will have at most 5,000 urban properties in its municipal head, some 4 large communities, but with less than 1,000 real estate and the rest rural area or as they call it of the Other side, rustic.

Cadastre for what. This is important to define, because the precision criteria for a cadastre with a legal approach will not be the same if the approach is only fiscal or control of land use. Also because if there is a Appraisal methodology, The measurement of buildings or valuation of the permanent crop requires other criteria to make the process more efficient.

The priority for a municipality that does not have a cadastre is not in its precision, it is in having it as a place to use it. So methods that are sustainable should be considered, that help to finish the complete survey of the municipality, to dedicate itself to using it, updating it and improving its precision.

Some methods I've tried.  The last four years we have tried different alternatives, depending on the conditions of the municipality, here I summarize some:

  • Photogrammetry.  Little by little, in urban areas this method is falling into disuse, mainly because it is not economical in relation to its precision. No company will make a flight at an altitude of 10,000 meters through a very small urban area, doing it for the entire municipality may be unattainable with its own funds. Therefore, if photointerpretation is used in urban areas, it is always necessary to measure the fronts and finally the precision will not be very good in areas where people pull out a knife by 10 centimeters. However, in the case of rural areas it is very practical because greater coverage is achieved without the need to go through each boundary and the precision is relatively sufficient since the plots have large areas. 
  • Photointerpretation + GPS. If you have the orthophoto, it can be applied perfectly to the rural area with very good results. To clarify, we are talking about an orthophoto from an aerial photograph, since the orthorectified satellite image that now has a pixel less than one meter has too many distortions in areas of irregular topography, for that grace it is better to use Google's orthography. In practice, I have observed that combining the use of printed (orthophoto) magnification and low precision GPS (Garmin 3 to 5 meters) brings more practical results than pinching aerial photographs and stereoscope and then moving to magnification. 
    I am not saying that they are disposable but questionable for projects of small municipalities, in their validity in the face of other facilities that now allow GPS with raster display or because peers or human resources capable of mastering the technique cannot always be available. The punching of photographs does not bring advantages in precision matters, because only the width of a rapidgraph on a 1: 10,000 printed orthophoto will be 10 meters plus the error that the orthorectification software has already accumulated. Also the question if the edge of a hill that the stereoscope shows very well but is not seen in a print, is discarded because practice shows that this is possible for a technician who comes from the conventional method, a novice will not see it for any of both methods and you will be better off taking a couple of GPS points to get your bearings. And then with the interpretation of other details like land use, current remote sensing techniques do better and cheaper work with supervised classification.
  • Cadastral survey methods GPS + Compass.  This method is very practical if you have little money. I've used it in urban areas, taking advantage of a pair of submeter precision GPS to process the street grid, and using a compass to tie off the ends. As tape is used to measure the fronts, the error is transferred to the street, leaving a relative precision of boundaries in less than 10 centimeters and absolute with respect to the moorings with GPS near the meter. You have to measure the funds and get the bearings with triangulation. It is not appropriate if the survey has legal implications, if property titles or cadastral certifications with legal value will be given; For that, it will occupy a field inspection at the time of application.
  • Cadastral survey methods GPS + total station.  This method is functional, because it allows very good precision and information in 3 dimensions that sooner or later will be useful. It requires a pair of GPS to georeference the first two starting points, and to take a few - enough - control points to prevent an error in taking the wrong back view. It is not necessary to have a total station, as it can be rented, as well as the GPS points that can be hired individually. The funds will always have to be measured, which can be supported by the orthophoto, compass or triangulation by moorings, which is the most appropriate.

Which I recommend.

If it were up to me to decide, for urban I would go by total station. Taking some kids out of high school in computing, training them, and releasing them to thrive works. Also for a municipality or association or consortium of councils, acquiring a total station that costs $ 7,000 is not a bad investment, since the use beyond the cadastre in surveying, stakeout or execution of engineering projects is a good investment. You just have to look for the training of human resources.

And in this I speak of a conventional total station, Robotics Does not apply to environments that labor is relatively cheap and where if you close half an eye they steal the station, the cell ... And if you still have the honor.

In conclusion, whoever decides the method must understand that the cadastral map will always be an imprecise reflection of reality. And as accurate as our current measurement is, in a few years Will be questioned By its relative imprecision with respect to a mountain of Mars.

The best method is the one that is sustainable with own funds, whose investment recovers in the short term and with which we will have the whole municipality raised in only two periods of government.

Golgi Alvarez

Writer, researcher, specialist in Land Management Models. He has participated in the conceptualization and implementation of models such as: National Property Administration System SINAP in Honduras, Management Model of Joint Municipalities in Honduras, Integrated Cadastre-Registry Management Model in Nicaragua, Territory Administration System SAT in Colombia . Editor of the Geofumadas knowledge blog since 2007 and creator of the AulaGEO Academy that includes more than 100 courses on GIS - CAD - BIM - Digital Twins topics.

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  1. My uncle died and I kiero change the name. And continue paying.

  2. The scenario is, therefore, a municipality, of regular size, that will have at most 5,000 urban properties in its municipal head, some 4 large communities, but with less than 1,000 real estate and the rest rural area or as they call it of the Other side, rustic

    4,787 urban real estate, 2,138 urban real estate in small towns, 18,000 rural acres.

    Yes, on this side and the other side of the puddle.

    Yes, in 8 years, with approval / agreement / presentation of securities in periods of 5 years and reinvestment of part of the funds obtained, if there is property tax.

    A larger municipality will occupy more silver, not necessarily more time.

  3. “Will we have the entire municipality raised in just two government periods?”

    How long is that, sir, a caterer?

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