Determining a mark layout across a patterning device or substrate

A computer program product comprising a non-transitory computer-readable medium having computer readable instructions therein, the instructions, when run on a suitable computer apparatus, configured to cause the computer apparatus to at least:

• obtain a model configured to model data associated with measurements performed on a patterning device or substrate at one or more mark positions across the patterning device or substrate;
• obtain an initial mark layout comprising initial mark positions;
• reduce the initial mark layout by removal of one or more mark positions to obtain a plurality of reduced mark layouts, each reduced mark layout obtained by removal of a different mark position from the initial mark layout;
• determine a model uncertainty metric associated with usage of the model for each reduced mark layout out of the plurality of reduced mark layouts;
• and
• select one or more reduced mark layouts based on the model uncertainty metric associated with the plurality of reduced mark layouts.