### distortion of map projections during long range projects survey

During land surveying for long range projects (500 km, as an example), we usually have problems with coordinate system management that is caused by distortion of map projections. To solve this:1. We can use 6-degree zone projection, but we need to include amendments into all our length measurements. It is uncomfortable and could cause calculations mistakes. Real lengths would be less or more than the lengths from project documentation. It is often impossible to explain to constructors what 1 meter from documentation is not 1 meter in reality.2. We can use dozen of projections with shifted origins, but it can cause inconvenience in using final data by projectors, managers, constructors, etc. Whole plan would be broken into sections.3. We can use 6-degree zone projection globally for project and additional local coordinate systems for such installations as bridges, stations, ets.4. If it is possible for project’s geometry we can select the projection that is going up to it, but this happens rarely I think.As for me, I used the third item for road construction. Do you have such experience and how did you solve this? Maybe you can name any other possibilities to solve this problem.

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#### Replies

• In this case you can do nothing to eliminate then distortion because you mast to use a projection system and all the projection system deform something (distance or angle or both) For a such a big project you can use the second option and brake the entire project in many section.
• I always employ geodesy and so is projection in all of my works. We, as surveyors, should always realize on field that every time we perform backsight observation, we are actually doing horizontal grid mapping by ensuring orientaion parallelism for all traverse stations in the entire project. We should always take into consideration convergence, scale factor values, and among other things to ensure reliability of survey result.

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