This dataset contains map layers in GeoPackage format with the following grids used in biodiversity surveys in the Netherlands: Layer name Size (m) Description IvonGrid Kwartierhok 1250x1042 Used between 1902 and 1950 by IVON botanical surveys. IvonGrid Uurhok 5000x4168 Used between 1902 and 1950 by IVON botanical surveys. Each square contains 16 'kwartierhok' squares with corresponding first four characters in column name. RdGrid Kilometerhok 1000 Used since 1950 in biodiversity surveys. Squares that fall within the same 5 km square have the same value RdGrid Uurhok 5000 Used since 1950 in biodiversity surveys. Each square contains 25 kilometer squares. The RdGrid maps are available in the WGS84 and RD New (EPSG:28992) spatial reference systems, as they are aligned to rounded RD coordinates. IvonGrid is only available in WGS84. Grid square codes Kilometerhok (1x1 km) and Uurhok (5x5) grids have corresponding grid square codes. A code consists of three concatenated numbers for map sheat (1-62), 5 km square (11-58) and 1 km square (11-55). E.g. a 5 km square code looks like 4017. In literature and on collection labels this often written as 40.17 or 40-17. Maintanance This dataset is being curated by FLORON Plant Conservation Netherlands since 1988 for use in botanical surveys (Theo Peterbroers, Bart Vreeken and Ruud Beringen). History IVON stands for "Instituut voor Vegetatie-onderzoek Nederland", an NGO founded in 1930 was most active until the 1950's and then succeeded by FLORON in 1988. More information about the repartition of the IVON grid can be found in Atlas van de Nederlandse Flora part 1 (Mennema et al. 1989). The original map was hand drawn on topographical maps by J.W.C. Goethart en W. J. Jongmans (Van Ooststroom 1956) originally following the Bessel 1841 projection (EPSG:7004). The grid cells are equal is size, although not rounded to kilometers. The size was probably chosen to fit maps that were commercially available at that time. References Mennema, J., Quene-Boterenbrood, Plate, C. L., Van der ...