In Belgium, (historical) biodiversity data often refers to two (nonstandard) grids for geolocation: IFBL and (so-called) UTM5.
The IFBL grid consists of 4km-wide squares over Belgium. Those 4km squares are also subdivided in 16 1km-wide squares. Details about the grid can be found on Atlas de la Flore de Wallonie : IFBL(in French).
UTM5 / MGRS5 is a non-official addition to MGRS. Each 10km MGRS square is divided into four, and a letter is added to the MGRS10 code. 'A' is the topleft quarter of the square, 'B' is topright, 'C' is bottomleft and 'D' is bottomright. An overview of the gris is presented at page 75 of "Voorlopige atlas en "rode lijst" van de sprinkhanen en krekels van België (Insecta, Orthoptera) / atlas et "liste rouge" provisoire des sauterelles, grillons et criquets de Belgique (Insecta, Orthoptera)"
Due to their nonstandard nature, data about those grids and coordinates conversion tools have often been difficult to find online. The Belgian Biodiversity Platform therefore decided to publish this data for reuse by others.
Belgium, with some buffer around (NE of France, W of Germany, ...).
OGC GeoPackages, one for each grid.
CC0, for maximum reusability.
- Conversions de coordonnées en Belgique (The University of Mons)