Half way: what a mess
I finally managed to change the code, so that now every new map that is created is first transposed to MySQL, and no big data is stored in the RAM. This was needed to permit bigger maps to be calculated. Also for the further versions of the mapmaker. Still the program is less then perfect. With all the work I did, it still did not manage to be able to compute data 6. Also all this use of MySQL is actually slowing down the performance for everybody else. Not clever. In the next days I shall work in adding indexes, and other changes that should make the code faster, and MySQL less subject to the weight of the mapmaker. I also need to look very carefully in the whole topic of the various character sets. Quite a lot of times the map is not being generated because the data are in the wrong character set.
I also noticed that it was not possible if you were not an administrator to make a map from some data that have not been uploaded by you. This was against the spirit of the site, so I corrected it, and now everybody can use everybody else data.