Every Feature belongs to exactly one project, and the projectId is what makes that link. Because a feature's featureNumber is only unique within its project, the projectId is essential for telling apart, say, Feature 3 in one excavation from Feature 3 in another. When you create a feature it inherits the projectId of the unit or site you are working in, and that value never changes afterward. Every artifact, photo, and stratigraphic record you attach to the feature shares the same project context, so reports and exports can gather a project's entire feature inventory cleanly.
Technical section
Data model, API, and internals — visible to developers.
