Isochore assignment confidence in border regions. (a) On average the isochore assignment confidence is lowest near borders. Here the borders of all isochore maps were used. Assignment confidence grows with the distance from the border and reaches saturation at a distance of about 0.2 Mb from the border. This can be considered as an empirically derived 'safe distance' threshold. (b) Variance of the assignment confidence is almost independent of the border distance.