A Feature always sits at one siteId, the archaeological site where the hearth, pit, or wall was actually encountered. This is more specific than the project: a single project can investigate several sites, and the siteId tells you exactly which one a feature came from. Relic sets the siteId when you create the feature from within a site context, and it stays constant. Because the site cannot be casually deleted while features still reference it, the siteId protects the integrity of your spatial record — you will not end up with orphaned features pointing at a site that no longer exists.
Technical section
Data model, API, and internals — visible to developers.