It shows the town’s defences at the time of the Spanish Armada in 1588. Its depiction of the town’s layout is not wholly accurate (the streets, for example, were laid out in a grid-like pattern), but the marketplace and St Nicholas’s Church are easily identifiable.
(click on image to enlarge) This image is taken from the British Library site which gives c.1585 as the date and refers only to "proposed harbour works". Source: British Library.
What are people with the large 'wheel' doing (blue number 1)?
What are the structures (blue numbers 2)?
Note: In case anyone is curious, the ship with the flag with black and white horizontal stripes would appear to be from the Belgian commune of Waimes