The coastline of penghu is crooked and lasts for 448,974 long. Except for the common cape bays, we can also see wave-erosion platform, wave-erosion cliff, wave-erosion cavity, sandy coast and rocky coast landforms along the coast area.

The lay of the isles are mostly gentle and almost every isle are surrounded by cliffs. The top is flat and no obvious ups and downs of the high mountains can be felt. It is a typical square mountain landform. The main reason to cause this landform is that the volcanos under the ocean have erupted with basalt flow. This flow came out with many layers of water-made rock formations of marine facies fossil. After many times of slow activities under the sea, a more flat under-ocean landform occurred. with a few more times of the change of the sea level, the landform is exposed in the air and has been eroded into what it looks like today and also becomes the most obvious landmark of penghu.
The lay of the lands slightly slides from south to north and the highest point is at 79m on "damow isle". Then going toward north by order comes 66m on isle chimay, 53m on wang-an, 52m on magong, 38m on baisa, 19m on jibay and 14m on mudow. It get's gentter going north to the Da-yao reef, and Er-yao reef...etc.