Hy-Brasil, much obliged!
Now that you delivered the key information, I could solve the riddle, check the map and reconnoitre the town and the way to write it in Chinese.
Now, what is so special about the postmark? It's my pleasure to show the whole item, which consist of four stamps altogether.

These stamps have been soaked off from an envelope which went from Taiwan to Germany. By the time I had contacts to a German exporting company which received mail from all over the world. I received numerous mail from that source and I noticed that the typical postmark on outbound mail in Taiwan is bilingual (Chinese and Latin characters). The postmark here only shows Chinese letters.
Also, the postmark consists of a dashed cirlcle, whereas the others in my possession all show a complete circle.
Nice as well is, that on the postmark typical Chinese Art is displayed where stamping in pieces of art was numerously used. The postal mark adds wonderfully to that.
I also deciphered the syllabels in the bottom of the mark which is ji zhi, but I can't derive a meaningful explanation from that.
By the way I checked on the effort to learn Chinese letter system which is supposed to be 2-4 times harder to learn, i.e. one needs more time to learn them than a Latin or Arabic system. I also had a look in a schoolbook, where even the way to write these letters was described in detail. It would take me at least 10 times the time to write a syllabel in comparison to a Latin word.
That is probably why I found one time very clear and detailed characters, which would take me hours to write. And another time there were much more simplified fonts, but these were nearly impossible to read for the lay person when compared with detailed specimen.
Taken everything into consideration, it seems rather adviseable to me to stay here in an English speaking forum, instead of joining a Chinese one (where - to make the confusion complete - all would sound Greek to me).