By 1625, most of the island was built up, as can be seen on the map of Amsterdam by Balthasar Florisz. van Berckenrode (image below). A few empty plots still exist, but they were probably not completely vacant. The historical documents contain some hints that some of these areas may have been in use as (timber) storage or work areas (unpublished notes Hans Bonke). Structures may also have been present that were not mapped.
Typically, a main house was constructed on the street side, and the back of the plot was left open or contained a smaller structure. This may have been in use as a garden shed, summer kitchen or rented out for living, storage or another purpose. In some cases the structure in the back could have a different owner than the main house on the street. Often they had their own way of access, through a small alleyway, sometimes crossing underneath the main house. The 1625 mapping suggests these structures are significantly smaller than the main house, and also had their roofs oriented on a different axis. In some cases, the pattern is reversed, a house is build on the back of the plot, but the front is left open, at least for a while. After a century, all plots on the streetside were also build up. The houses were used for habitation, but many inhabitants were small business owners and had their (work)shop on the street side. People living in the back houses as tenants, had different professions which did not require them to have street side representation.
The space in the center of the block was largely open, and remained so for a long time. On the 1625 map, it is suggested they were used for gardens. What exactly was grown there is not known, but we may suppose that the population of Vlooienburg made both kitchen gardens as decorative flower gardens. This difference may be indicated by the different garden bed patterns drawn by the cartographer. This is distinct from the inner city, where most space had been built up and hardly any private gardens existed. The more one moved to the edges of the city, the more garden space was available.