A method for evaluating an orientation of a molecular array having features arranged in a pattern. An image of the molecular array is obtained by scanning the molecular array to determine data signals emanating from discrete positions on a surface of the molecular array. An actual result of a function on pixels of the image which pixels lie in a second pattern, is calculated. This actual result is compared with an expected result which would be obtained if the second pattern had a predetermined orientation on the array. Array orientation can then be evaluated based on the result.