A nice park when you come from the river and are heading up the Jade Emperor Hill. The layout becomes obvious once you climbed the many stairs up the hill and have a view down onto the park.
Best description I found:
>>Although the octagonal shaped field is made up of eight pieces of land, with a symbol of Yin and Yang in the middle, you will not be able to distinguish it at ground level. I recommend ascending the Jade Emperor Hill for a bird’s eye view of the Eight Diagram Field. [...]
The Eight Diagram Field was formerly used for rituals by emperors to pray for good harvest in ancient times. Today, each piece of land is used to grow a different crop like soybean, barley, wheat, millet, and glutinous rice, just to name a few. However, there are times when the farmers grow sunflowers, rapeseed, and other colourful blossoms. You can always check with the locals before visiting this field when you’re in Hangzhou.
Apart from taking a leisure stroll around the field, or a short hike up to the peak of the Jade Emperor Hill, you can also wander around the streams and temples around the area.<<