The Zeeland grid is a composite depth grid based on the depth information in the Inland ENC of Zeeland. The grid is composed of +/- 1150 soundings. The actual number of soundings differs per edition of the Zeeland grid. The accuracy depends on the type of sounding on site, the most accurate sounding is the multibeam sounding. These meet the IHO special order standard. The entire grid is produced in UTM(31) projection and then transformed to R.D. The vertical reference is the N.A.P. Due to the transformation from UTM to RD, an additional deviation occurs in the bottom height. This deviation is virtually random and different for each grid cell. This extra deviation in height is within 15 cm for 99% of the grid. With a soil with a very steep slope, the deviation can be up to 2m. Cells with a very different depth are always isolated grid cells. In the surrounding grid cells, the deviation is much smaller, so that a correct soil image remains visible. The Zeeland grid can be used as an indicative grid. It is not suitable for navigation, for checking other soundings or for volume calculations. This due to the transformation of UTM31 to RD.
