What Makes A Valid US Style Crossword Grid?
With US grids, every white square in the grid is checked. The term "checked" means that it appears in both an across and a down clue, so the one 'checks' the other: if you aren't sure what the answer is from an across clue, then you can get it from the down clue that checks it, or vice versa, depending on your interpretation.
As such you have two chances to get each and every letter in the grid, and therefore you can theoretically solve the puzzle from just all the across clues or all the down clues: in theory you never have to look at both sets of clues. Whether anyone ever has done, or does, solve puzzles from just one set of clues would be quite interesting. Certainly when you look at easy US crosswords then it would definitely be possible and realistic to solve the puzzles this way. With the harder sort of puzzle that you get in newspapers, whether this could be done is more doubtful as normally you need to work both sets of clues to have a chance of finishing the puzzle successfully.
The grids have radial symmetry - that is 180-degree rotational symmetry. They also have a much higher percentage of white / answer squares than black / shaded squares. Certain newspapers will have strict limits in place as to how many black squares are allowed in a grid, and sometimes they disallow them forming 2x2 blocks, for instance.
Typically two-letter words are banned in grids, and some put limits on word lengths and the total number of clues allowed in the grid. With a US crossword, usually the answer lengths are left out, and if the answer is made up of multiple or hyphenated words, this is not indicated - it is up to the solver to work this out, which can make those clues trickier.
As for grid sizes, most publications enforce the rule that the grid must be of odd dimensions, with 15x15 being the most common for daily puzzles. Some even have set patterns that compilers need to work from.
Date written: 01 May 2015
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