Where every number comes from

How the numbers are made

Sampling

Each place, monument and summit is sampled at its own coordinates. Temperatures, precipitation and cloud cover come from the 1 km CHELSA grid cell containing the point. CHELSA temperature and precipitation continue across the coastline; for cloud cover, where a coastal point falls outside the land grid, the nearest land cells within a 7 × 7 window are averaged. Mountain summits use the cell around the summit, which represents the summit area; on sharp peaks the very top is usually a little colder than the cell average.

Station correction of highs and lows

CHELSA's average daytime highs run cooler than weather-station records in much of Europe and the United States: in July by 1.6 °C on average at the stations in our European countries and by 0.9 °C in the U.S. We therefore compare CHELSA with the 1991–2020 normals of about 13,300 stations, including the national climate networks of Germany, Austria, Switzerland, France, the Netherlands, the United Kingdom, Ireland and Spain and regional networks in Italy and Spain, and carry each station's difference over to the places and summits around it. The closest stations count most, stations at a very different height count little, a station also counts little where its grid value differs strongly from the place's own (so the sea-cooled cell of an island station does not warm towns on the mainland), and the adjustment fades to zero at 150 km; places farther than that from any station keep the CHELSA value. Tested by leaving out each station in turn and predicting it from the others, the typical July error falls from 1.5 °C to 0.6 °C. The national and regional networks matter most in towns and valleys: at their 4,500 stations the remaining July error drops from 0.82 °C with the synoptic stations alone to 0.59 °C, in Italy from 1.22 °C to 0.68 °C and in Spain from 1.15 °C to 0.84 °C. The Emilia-Romagna series start in 2006 and the Basque series end in 2015, so their averages lean slightly towards a warmer and a cooler part of 1991–2020. Because the station normals cover 1991–2020, adjusted values reflect that more recent period. Night-time lows are adjusted the same way; in the U.S., where CHELSA nights run about 1.8 °C warm, the typical error falls from about 2 °C to under 1 °C. Where a station's ready-made 1991–2020 average is missing (for example Porto, Faro or the Azores), we average its monthly reports for 1991–2020 when at least ten years are available. On low-lying islands and coasts the CHELSA cell is largely sea and can be several degrees too cool in summer (Zakynthos +7.9 °C in July), so differences of up to 8 °C are accepted there, against 6 °C elsewhere.

Month score

The sightseeing score (0–100) combines three parts: temperature comfort (42%), which is full for average daytime highs between 18 °C and 25 °C (64–77 °F) and falls to zero at 10 °C and 35 °C; dry days (33%), equal to 1 − wet days ÷ 14 (or 1 − precipitation ÷ 120 mm where wet days are not available); and clear skies (25%), equal to (90 − cloud cover %) ÷ 60, capped between 0 and 1.

The beach score uses comfort for highs between 25 °C and 31 °C (35%), sea temperature between 21 °C and 28 °C (25%), dry days (25%) and clear skies (15%). It is only calculated where we have a sea temperature. The best months shown for each place are its three highest-scoring months.

Climate type

The Köppen–Geiger class is computed from the same monthly normals using the standard thresholds (Peel et al., 2007 variant with a 0 °C boundary between temperate and continental climates).

Similar climates

Places are compared on their twelve monthly highs, lows and cloud cover. The closest matches at least 150 km away are listed, with a match percentage derived from the root-mean-square difference.

Which places have a page

A place gets a guide when it has at least 1,000 inhabitants (or 300 with an encyclopaedia article, or a documented village with a photograph and a monument or summit nearby) and enough data to be useful: population, a photograph, monuments or summits nearby, or an airport within 100 km. Separate climate guides and month-by-month pages are created for the places travellers look up most: towns above 50,000 people, and well-documented smaller towns and coastal resorts. Monuments need a recorded protected status, a photograph and at least one documented fact such as a date, an architect or a style (World Heritage sites always qualify when documented). In continental Europe this includes monuments described only in the country's own Wikipedia, so some names appear in the local language. Lakes, waterfalls, glaciers, national parks and mountain huts need a name and either an encyclopaedia article or a photograph with a recorded size or height; surface areas and heights use the unit-normalised values, and lakes that no longer exist are left out. Mountains need climate data and an article, a photograph or 300 m of prominence.

Daylight

Sunrise, sunset and day length are calculated by us with the NOAA solar position algorithm for the 15th of each month, using the official 90.833° zenith.

Mountains: snow and freezing level

Snow months are those in which the summit's mean temperature is at or below +1 °C with at least 10 mm of precipitation. The average freezing level is estimated from the summit's monthly mean temperature with a standard lapse rate of 6.5 °C per kilometre. Topographic isolation is the distance to the nearest higher summit in the atlas, left blank above 300 km where a higher peak outside our countries may be closer.

Wildlife

For each country we take the most recorded species of each group and count published records per calendar month. Months with the most records are shown as the best time to look. Record counts reflect both the animals and the people recording them, so busy holiday months can be over-represented.

Routes: line, profile and walking time

Each route's line is put together from its OpenStreetMap ways, following their shared end points; where the mapped route has a gap, the pieces are joined and the gap is left out of the length. The two Portuguese ways to Santiago are mapped in many separate sections, so their line is found through the ways of all Portuguese Camino routes, by way of the towns each way is known for. Heights come from Copernicus DEM GLO-30, read every 20 m and smoothed with a three-point running median; climb and descent count only changes of more than 2 m. Checked against 890 official Swiss stages, the climb was off by a median of 7.7%.

Walking time follows DIN 33466: 4 km an hour on the level, 300 m an hour uphill and 500 m downhill, taking the larger of the horizontal and vertical times and adding half the smaller, without breaks. Official Swiss routes show their official time and climb. For cycle routes we assume a relaxed 16 km an hour plus 8 minutes for every 100 m of climb.

Routes: grade, effort and months

The technical grade uses the SAC hiking scale (T1–T6): the highest grade mapped in OpenStreetMap on at least 5% of the route or, in Switzerland, the official path class (hiking trail T1, mountain trail T2 or T3, alpine route T4). Effort combines time and climb: easy below 2 hours and 300 m of climb, moderate below 4½ hours and 800 m, demanding below 7 hours and 1,400 m, very demanding beyond that; more than 10 hours of walking counts as a multi-day route.

Each month is rated with the climate at the route's highest point: the nearest atlas place or summit with climate data, adjusted to that height by 6.5 °C per kilometre. A month is good when the average high is 8–26 °C and it is no wetter than the route's median month, good but wetter when only the rain is above it, possible with highs of 3–8 °C or 26–30 °C, and unsuitable otherwise. On routes that climb above 1,800 m only June to October can be good, because of snow.

Suggested stages on the Camino de Santiago

The Camino has no fixed daily stages. We cut each way at villages within 1 km of it that have an albergue or hostel in OpenStreetMap or at least 1,000 inhabitants (GeoNames), aiming at about 23 km a day and keeping between 18 and 28 km where the villages allow it; every 300 m of climb counts as one extra kilometre, and larger towns are preferred as stage ends.

Direction, country and lists

A route runs the way its OpenStreetMap from and to tags say (or Wanderland's start and end); otherwise it starts at the end near the better-known place, a station, a stop or a car park. Its country is where most of its length lies. A town's list of hikes holds the hiking routes that start within 10 km of it or pass within 3 km; a park's or a lake's list holds the routes linked to it.

Photos on route pages are the atlas photos of the summits, huts, lakes, waterfalls, sights and villages the route passes; where there are fewer than three, Wikimedia Commons files within 200 m of the line are added after the same licence and quality checks. At most eight per route, spread along it.

Which routes are indexed

Every named route has a page. Search engines are asked to index it only when it is at least 3 km long (10 km for cycle routes, 5 km for stages), its line has no real gaps, and at least two of these apply: an official, national or regional network; a Wikidata or Wikipedia entry; photos; at least three atlas places, summits, sights or nature areas along the way; a start within 3 km of a town with a page. A town's list needs at least five such routes, a park's or a lake's at least three. GPX files carry the line, our heights and the drinking water and huts along the way. France's GR® routes have no GPX download, as their tracks are kept by the Fédération française de la randonnée pédestre.

Units

Pages for the United States show °F, miles, feet and inches; all other pages use metric units. The °C/°F switch at the top of every page changes temperatures everywhere and is remembered on your device.