jats:titleAbstract</jats:title> jats:pBulk, single grain RE–Ba–Cu–O (where RE = rare earth or yttrium) [(RE)BCO] high temperature superconductors could potentially be used to generate stable magnetic fields for magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR). In these applications, however, the homogeneity of the magnetic field is of critical importance. As a result, the spatial distribution of critical current density, jats:italicJ</jats:italic> jats:subc</jats:sub>, within the bulk single grain and the effects of the magnetisation process, which are primary drivers of the uniformity of the achievable trapped magnetic field, are fundamental to assessing the performance of these technologically important materials. This paper reports the systematic measurement of the distribution of jats:italicJ</jats:italic> jats:subc</jats:sub>–jats:italicB</jats:italic> at 77 K over a vertical cross-section of a single grain along a facet line and through the seed crystal [(110)-jats:italicF</jats:italic>] at 20 positions within a 20 mm diameter Gd–Ba–Cu–O sample in an attempt to understand and assess the distribution of jats:italicJ</jats:italic> jats:subc</jats:sub> along this microstructural feature. A comparison of the data within the whole vertical plane across the seed measured along the jats:italica</jats:italic> or jats:italicb</jats:italic> direction within the [(100)-jats:italica</jats:italic>] plane shows that jats:italicJ</jats:italic> jats:subc</jats:sub>–jats:italicB</jats:italic> at 77 K at the facet line is more than 10% higher for applied fields between 0.2 T and 2.5 T. The effect of the jats:italicJ</jats:italic> jats:subc</jats:sub>–jats:italicB</jats:italic> relationship of the facet line on the overall trapped field measured in an individual bulk sample was investigated by measuring the magnitudes of trapped fields and their contour maps for sections cut from four single grain samples of GdBCO–Ag at different sizes and shapes parallel to the jats:italicab</jats:italic>-plane from the top to the bottom of the bulk sample. Based on the results reported here, we demonstrate a method to achieve more uniform trapped fields through an optimal arrangement of an assembly of sections of individual GdBCO single grains.</jats:p>