In geography, a chart without annotation is a decoration. We steal that habit. Along every retention table we keep a second list: store incidents, payday calendars, a marketing blast that should have been a footnote, a celebrity who mentioned the category but not the brand. The list is dated. It is allowed to include things that made the curve look better. Flattering weather is still weather.
Birth matters more than people admit. A cohort born on ‘install’ and a cohort born on ‘first core verb’ will not share a climate. Mixing them is how a team ends up arguing past each other with identical-looking N-day plots. The Atlas forces a written origin line before colour is applied.
Three cuts, then stop
Channel is a magnet for fishing. We delay it. First platform, first successful task, and country of first session usually explain more, and they survive a sceptical director. If a cut cannot be explained to support in one sentence, it stays out of the pack even if the p-value looks charming.
Mobile Session Cartography adds another front: background fetch dressed as a return. iOS and Android do not share a definition of presence. A ‘healthier’ iOS curve we studied was a costume of silent wakes. The weather metaphor helped; the team stopped congratulating a climate they had not caused.
If you want to practise this on a live artefact, bring it to Retention Signal Studio. If you only want the map, start on the Cohort Atlas page and write the origin line before you open a tracker.