Why do we need an open space map? The Agency for Nature and Forests (ANB) only allows the hunt for partridges in an area if several conditions are met. One of these conditions is that there are enough partridges present. For this, ANB applies a minimum of 3 breeding pairs per 100 ha of open space. Therefore, a game management unit (GMU) that wishes to hunt partridge must first make an inventory of where all the partridges occur in the GMU. Based on these observations, the Research Institute for Nature and Forest (INBO) determines the number of breeding pairs in each GMU. Finally we divide this number of breeding pairs by the area of open space to get the density of partridge (number of breeding pairs per 100 ha open space). To obtain the area of open space in each GMU, we need a map that defines what open space is. Why a new open space map? After the spring 2021 censuses, several hunters informed us that the current open space map does not always correspond to reality. Some plots were classified as open space on the map but are a built-up or forested area in reality. This overestimated the area of open space and underestimated the density of partridge. The previous version of the open space map is based on the most recent publication of the biological valuation map (BVM). Although this version of the BVM was published in 2020, it does not mean that all the information originated from 2020. Actually, about three quarters of the information turned out to be older than 2007. For that reason, we went looking for a better source. An open open space map After weighing a number of options, we chose OpenStreetMap as our source map. Like all other candidates, this map is not perfect. However, it is good enough to use. And it has the advantage that errors are relatively easy and quickly corrected. At the start of the surveys, hunters are given a preliminary version of the open space map. When hunters identify errors in the open space map, they can report the error or modify it themselves in OpenStreetMap. After calculating the number of breeding pairs, we can generate an updated version of the open space map based on the most recent information from OpenStreetMap. This update ability is an important difference between OpenStreetMap and other usable maps. Furthermore, the other maps are based on information that is at least 1 to 2 years old. For hunters, this way of working provides them the opportunity to contribute to a correct open space map themselves. Since OpenStreetMap provides the information with open use terms, everyone can enjoy an improved OpenStreetMap. A reproducible open space map In this report, we describe how to convert the information from OpenStreetMap to an open space map. We established the conversion as a computer program. We publish that computer program together with the open space map and the source maps that were used (OpenStreetMap and hunting area boundaries). In this way, everyone can check the rules (or have them checked), use, or implement them themselves.