A Czech number is nine digits dialled whole, with no area code since 2002 — but a landline's first two digits still say where it is, because the plan gave every region a prefix or a few: 2 is Prague, 37 Plzeň, 55 and 59 Ostrava's region. This map draws each region in its prefixes, coloured by the first digit: 2 the capital, 3 and 4 Bohemia, 5 Moravia and Silesia.
How to read the map. Each patch is a region and the numerals on it are the digits its landline numbers begin with — one prefix for most, two or three where the region is large: 31 and 32 for Central Bohemia, 38 and 39 for South Bohemia, 41 and 47 for Ústí nad Labem, 51, 53 and 54 for South Moravia, 55 and 59 for Moravia-Silesia. Prague's numbers begin with 2 alone. The colour is the first digit: 2 is Prague, 3 the centre, west and south of Bohemia, 4 its north and east, 5 Moravia and Silesia.
No area code, still a geography. The plan of September 2002 closed Czech numbering: the trunk 0 went, every number became nine digits, and there is nothing to leave off when dialling from next door. What survived is the first pair of digits, which the plan handed out region by region, and the third digit below it still tends to follow the old districts — 311 is Příbram, 312 Kladno — though no published list fixes that below the region, and the map does not pretend to. The regions are the Czech Office for Surveying's, as geoBoundaries publishes them.
Sources. Prefixes: Wikipedia, Telephone numbers in the Czech Republic — the prefixes of geographic numbers by region. Geometry: geoBoundaries, Czechia ADM1 (simplified), from the Czech Office for Surveying under CC BY 4.0; dissolved by zone.