Project sync

A Mapit project is a GeoPackage: one file holding the layers, the forms behind them and everything collected into them. When a project goes to the cloud that file stays what it is, and the copy on the server is the one everybody converges on. Nothing is shredded into a database that can only be read back through us, which is why the answer to “can we have our data” is a download rather than a support ticket.

What travels is not the file. A phone that already holds the project sends the rows it changed and receives the rows everybody else changed, so the first sync moves a project and every sync after it moves a conversation. That is why the second sync and the two hundredth are both small, and why a crew on a thin connection at the end of a long day gets their work away rather than watching a progress bar.

Two surveyors open the same lamp post. One corrects the height, the other records the lamp type. Row-level sync makes that a fight and one of them loses their afternoon; here both land, because the server works out which columns actually changed and applies each one. The geometry counts as a single field, since half a position is not a position.

When the same field really is set to two different values, the first to reach the server stands. That rule is chosen rather than convenient: the alternative is letting a device clock decide, and phone clocks are wrong often enough that “the later edit wins” quietly means “whoever’s time zone was mis-set wins”.

The discarded value is not discarded. It becomes a conflict record carrying both sides, which device sent each and when, and a manager reviews them in the portal. A sync may make a decision; it may never make work disappear. Editing a feature somebody else deleted is the same story from the other end: the deletion stands and the edit is kept, rather than a row quietly coming back to life.

Jobs change. In week two somebody needs a column that was not in the original form, and on most systems that means a new file for everybody and an evening of making sure nobody is still holding the old one. Here a manager edits the structure, releases it, and the change travels as a patch: the phones apply the new column and keep everything already in them, including work collected that morning and not yet sent.

Additive changes go through. Renaming a field, retyping one, or dropping a layer that people are still collecting into is refused at release with the reason, because those are the changes that strand work, and a refusal you can read beats a migration you discover afterwards.

The app works with no account and no signal; it did before any of this existed. Sync is something the project does when there is a connection worth using, and nothing about collecting waits on one. A push is never refused because a project is close to its size limit either: the crew did not set the quota, and destroying a day of fieldwork over somebody else’s billing rule is not a trade we are willing to make. The manager gets warned instead.