I've got geotiff 20x30 pixels (obtained from ENVI "save as") for which ENVI generated the world file tfw: 0.5 0 0 -0.5 20.25 49.75 So 49.75 is the uper left pixel center value (i.e. according to https://en.wikipedia.org/wiki/World_file) the tiff file has also geotags (dumped with exiftool): Pixel Scale : 0.5 0.5 0 Model Tie Point : 0 0 0 20 50 0 Geo Tiff Version : 1.1.0 GT Model Type : Geographic GT Raster Type : Pixel Is Area Geographic Type : WGS 84 Geog Linear Units : Linear Meter Geog Angular Units : Angular Degree when I export this file to ASCII Grid format (ESRI) it has in header yllcorner 35.500 As one can simply calculate from world file: yllcorner = ylrcenter - "pixel size in the y-direction"/2 - (ysize -1)*"pixel size in the y-direction" = 49.75-0.5/2 - (30-1)*0.5 = 35 so yllcorner 35.500 is corresponding to the upper boundary of the lower left pixel, it's not the correct yllcorner value! (I guess someone missed -1 in the formula)