TTDI Best Cities Index — methodology
Ranked from measured data refreshed on a fixed cadence; the scoring thresholds are methodology choices, disclosed below.
The month-fit score
Each edition ranks cities for ONE calendar month. The score blends three pillars: climate comfort at 60%, the month's event density at 25%, and daylight at 15%. When a pillar has no data for a city — a city without events-feed coverage, for example — the remaining pillars are re-weighted; a missing feed is never scored as a quiet month.
Climate: bands refined by measured rain hours
The climate pillar starts from the same four comfort bands the Best-Months Heat Map discloses (ideal 100, good 70, mixed 40, difficult 10) and refines them with hourly reanalysis: minus 4 points per hour of perceptible rain per day (at least 0.5 mm/h — trace drizzle is filtered), floored at −20, plus up to 10 points when more than 70% of mornings (07:00–12:00 local) stay dry. Cities whose hourly signals are not yet measured keep their band score untouched.
Events and daylight
The events pillar is the city's percent-rank by number of catalogued events in that calendar month, among cities with events-feed coverage. The daylight pillar is astronomical day length at mid-month computed from the city's latitude, scaled from 8 hours (0) to 14 hours (100).
Twelve editions a year
Every month is its own frozen edition at its own URL — citing the July edition stays accurate forever, and the landing page always shows the month you are in.
The universe
Each edition ranks every city TTDI covered at the moment the edition was cut — the cities whose pages we publish and stand behind. The universe size is stated on every edition; an edition is never cut over fewer than 12 qualifying cities. As coverage grows, later editions rank more cities.
How ranks are assigned
Ranks are competition-style: cities with equal values share a rank, and the next distinct value resumes at its ordinal position (1, 2, 2, 4). We never separate tied cities alphabetically — a tie is reported as a tie.
Editions are frozen
Every edition is a frozen snapshot: once published, its ranking never changes, so a citation of this edition stays accurate. Updates ship as new editions at their own URLs; prior years remain available.