Almost everything known about this meeting comes from two passages, and they are difficult to reconcile. Acts 15 describes a formal assembly at Jerusalem with speeches, a presiding judgment from James and a circulated decree. Galatians 2 describes Paul going up to Jerusalem by revelation, meeting privately with those reputed to be pillars, securing agreement that he should go to the gentiles and they to the circumcised, and being asked only to remember the poor.
The differences are not small. Paul mentions no decree and no food regulations, which is awkward, since in the same letter he is arguing precisely about such things and a ruling in his favour would have helped him. He also describes a subsequent confrontation with Peter at Antioch over eating with gentiles, which reads oddly if the question had just been settled in council. Acts, for its part, presents a harmony among the apostles that Paul's own letters do not support.
Scholars have proposed that the passages describe the same meeting from different angles, that they describe two different meetings, and that the decree in Acts reflects a later settlement retrojected onto an earlier occasion. None of these can be tested, because there is no third source. The atlas records the meeting because both texts attest something, and records the discrepancy because a reader who meets only the smooth version in Acts will be surprised by Galatians.