The big picture
Oolong grows along a coastal arc roughly 23 to 28 degrees north, from Fujian through Guangdong to Taiwan.
Fujian holds two of the four great districts, and they could hardly be more different from each other.
Wuyi sits in the mountains on the Jiangxi border, where red sandstone cliffs form narrow gorges.
Anxi lies further south and closer to the sea, on rolling hills around 300 to 1,000 m.
Guangdong contributes Fenghuang, in the hills above Chaozhou, where single bushes are picked and made separately.
Across the strait, Taiwan grows oolong from Nantou in the centre to Chiayi and Taichung further north.
Those districts sit at 1,000 m to 2,600 m, which is higher than almost anywhere on the mainland side.
Four clusters, one category, and the distances between them are short enough to fit on a single map.
What separates them is not distance but the combination of cultivar, elevation and local method.
Each district settled on a different way of handling the same partly oxidised leaf.
The map is therefore a map of techniques with climates attached, rather than a map of one plant.
Reading the map
Read the map by mountain system rather than by province, because the province lines explain nothing.
Fujian alone contains the Wuyi range, the Anxi hills and the northern border with Zhejiang, each with its own tea.
Wuyi’s core rock area covers only a few dozen square kilometres, and leaf from outside it sells as a lower grade.
That is unusual in tea, where most origin terms cover far more ground than buyers imagine.
Anxi is bigger, and the county produces far more tea at a much lower average price.
Plot the two and you see the pattern: a small high value centre surrounded by a large volume of ordinary leaf.
Fenghuang works the same way, with Wudong Mountain at the top and the surrounding townships below it.
Taiwan inverts it, since high elevation there is the rule rather than the exception.
Alishan, Lishan and Dayuling are all above 1,000 m, and the highest gardens reach 2,600 m.
Elevation is what the Taiwanese names are actually selling, more than any particular valley.
So clusters rather than a spread, and each cluster has a centre worth more than its edges.
Why geography matters
Geography reaches the cup through three channels: climate, soil, and the method that grew up locally.
Climate is the strongest, because temperature and cloud cover set how fast the leaf grows.
Slow growth at altitude produces a thicker leaf with more of the compounds that make tea taste sweet.
That is why Taiwan high mountain tea tastes soft and thick without much processing skill being involved.
Soil matters most in Wuyi, where the weathered sandstone gives the mineral note the region is known for.
The same cultivar planted outside the range loses much of that character, which growers will confirm.
Rainfall patterns matter too, since the coastal districts get their moisture from the summer monsoon.
Method is the third channel, and it is the one people forget when they talk about terroir.
Roasting became standard in Wuyi partly because a damp mountain climate made storage difficult.
The technique answered a geographic problem, and it is now sold as a matter of taste.
Move the leaf and you lose all three at once, which is why transplanting rarely works.
A starting point
Use the map as a skeleton and hang everything else on it, rather than learning names in isolation.
Start with the four districts, and learn one tea well from each before going further.
A Wuyi roast, an Anxi ball, a Fenghuang dancong and a Taiwan high mountain cover the range.
Four cups is enough to feel how wide the category is, and it costs less than a single expensive cake.
Then add altitude, which separates the Taiwanese gardens and the high slopes of Fenghuang from the rest.
Add the GI designations after that, since they tell you which boundaries are legally drawn.
Regional difference is the last layer, and it makes sense only once the districts are fixed in your head.
Reading a label becomes easier with the map in place, because most claims are about position within it.
Zheng yan（正岩）, single tree and high mountain are all statements about where on the map a leaf came from.
Each is checkable in the cup to some degree, and each is routinely overstated on packaging.
Learn the geography first and the marketing gets easier to discount, which is most of the battle.