Feature locations in array reading

Feature locations are determined in an array image obtained from reading a chemical array comprising multiple features arranged in a polygon and which array optionally includes sub-arrays within the array. A complete image of the array or a sub-array is presented on a display. Magnified images of corner regions of the displayed complete image are simultaneously presented on the display with the complete image. A user selection of corners for the array or sub-array are received and an array or sub-array actual outline is generated by linearly connecting the user selected corners. The generated actual outline is presented on the magnified image and may also be simultaneously presented on the complete image. Feature locations in the array or sub-array image may be determined based on the actual outline.