The question this page answers
Which of a source's sets does Tightly read, who is right when two sources describe the same thing, which source column feeds which Tightly field and how is it transformed on the way, and what changes if I save? Data mapping is not a page of its own: it is a wizard reached from a connector page on Integrations, where a set's Match the fields act opens it on that set's fields. The NetSuite purchasing card and a store's collection mappings open it the same way.
What you see
The rail carries four steps and never marks one done: Choose the data, Who owns what (only where a set you ticked is already described by another source), Match fields and Review. The faces under them are Choose the data, Who owns what, Match the fields (the sample, then the rows), Values, and Review and save.
Each face's head is its name, the figures beneath it and, where there is one, the time the choice was last saved. No sentence judges the step back to you.
Choose the data is one table: Set, On file (the rows Tightly holds at the set's grain, or Not counted), Already fed by (the other sources describing it, or Nothing else) and Read, the tick. A set this connector cannot send reads Not sent with the server's reason on hover. Ticking a set turns on the sets it reads from, and unticking one turns off the sets that read from it. Beside the table, Switches on lists the engines the saved ticks run, Runs or Degraded. Who owns what is one card per set described twice, with Who is right, the served Suggested mark and the consequence of saving, such as "{sets} re-read from the new owner on the next sync; nothing is deleted."
Match the fields reads the sample first: one row per set with Columns found, Records read, Fields, Matched and Review, and the figures Matched, Need a decision and No source, each opening the rows it counts. Then the rows: each is a source path with values from the sample, the Tightly field it feeds, a confidence word (Certain, Likely, Unsure or Nothing found) with the evidence For and Against, and the acts Confirm, Use this or Do not import it. Values rows read Matched, Set by you or Review. Review and save groups the changes as Stops a set loading, Moves numbers people are watching, Adds coverage and Quiet changes, with What runs again beside them: Tonight, On next open or Unchanged.
Three drawers open from a row. Transform shows the field's contract, where it starts from, the steps applied to it, each switched on or off, the result on your actual rows, and a line such as "{n} of {m} rows produce a usable number". Grain shows how one value per supplier spreads to every variant and place, with bridges tagged Simplest, A default you can override, More accurate or Degrades an engine, and Recommended beside whichever one the server recommends. Pick who is right settles which source wins a field.
The absence words are Not sent, Not counted, Nothing else, Queued, Reading, Not read, Never saved and Not measured.
What to do
Tick the sets to read and save. The page answers "Saved. This records how you want the connection sourced; syncs are not filtered yet." Saving records the choice as a version; only where Tightly has switched scoped syncs on for your workspace does a set turned off stop being fetched from the next sync, and what it already brought stays. Where two sources overlap, pick the owner per set and save; the page answers "Saved, re-read on the next sync." Confirm the matched fields, one at a time or with Confirm {n} likely; open Transform where a unit or a format needs changing, where the line before its button reads "Saved as a versioned rule; revert it from History."; open Values where a scale is mixed. Then Review: Save and apply publishes one version for each set that changed, and the receipt renders where the button was. Until you press it, "Nothing recalculates until you save."
Members draft; only admins publish and revert, because a publish restates numbers other people read. A member reads "Saving a mapping needs an admin; ask one on Team." where the button would be. Every save is kept as a version and an admin may revert one, but no page offers Revert yet.
On Tightly Connect, the sell-out intake has a Map step of its own: it appears only when nothing recognised the file, and publishing it makes that account's next file read itself.
Tightly matches deterministically: the same sample gives the same rows every time. Proposing matches writes only a draft; nothing is published until Save and apply.
When it is empty or failed
Before a completed sync there is no sample, and the wizard prints the server's sentence: "Tightly has not read a sample from {source} yet." An address with no connection in it reads "There is no connected system at this address."; one naming a connection you do not have prints the server's refusal. A save that lost a race reads "Somebody else saved this first; read it again before you save." A failed read prints the server's own sentence where one was written, and never a figure.