An "American crossword" refers to a particular type of word puzzle featuring a square grid of varying sizes and a series of clues to use to fill in the squares in this grid with letters. The puzzle originated in 1913, when Arthur Wynne published the first crossword on American soil in the New York World. Over time, the American form of the crossword has evolved differently from the British one.
In an American-style crossword, the grid is a large rectangle, almost always a square, filled with smaller squares. The internal squares are all of the same size and are alternately black-filled or white and empty. The grid is very similar to those in other types of crosswords, including those of the British style.
Grid Symmetry and Pattern
An American crossword grid often features some degree of symmetry of the pattern of black and white square coloration. Many grids feature left-right symmetry; many more grids demonstrate 180 degree rotational symmetry. This is primarily done to create a more visually appealing puzzle.
Unlike British-style crosswords, however, alternate squares in American crosswords are not blackened. With American crosswords, there are generally large spaces of adjacent white squares, with the black squares usually serving to generally separate the puzzle into nine or sixteen small regions of white squares, with some space to allow linking between the small sub-regions. This allows the clues, when filled in, to have their letters be tightly interlocked. This is a key attribute of the American crossword, as there are generally no unchecked squares in a grid; except in rare cases, each empty square constitutes a portion of both an "across" and a "down" answer.
Composition of Internal Squares
The black squares and most of the white internal squares feature no marking at all. However, when white squares have a black square or an edge of the puzzle above them or to their left, the square includes a small number in the upper left of the square. This number refers to the clue that is used to fill in that square and each subsequent white square to the right of or down from that square.
Each square that contains a number in the grid refers to a clue below. The clues are separated into two general groups, usually called "across" and "down," which indicate the direction in which the answer to the clue will fit into the grid. Generally, if a blank square with a number in it has an empty square to its' right, there will be an "across" clue matching that number; alternately, if there is a empty square below a square with a number in it, there will be a "down" clue matching that number.
The largest difference between British and American crosswords is in the clues: in American puzzles, the clues are much more straightforward, often involving strict word-definition relationships or specific cultural references, whereas in British puzzles, the clues are generally much more cryptic. In general, the difficulty in American crosswords comes with the fact that quite often multiple answers fit the number of spaces given for the clue. Given the highly interlocked nature of the grid, however, one usually fills in the very specific clues with only one answer first and then uses these letters where they cross other answers to aid in coming up with an answer to the clue.
Here are three sample clues from American crosswords that provide a good overview of the types of clues that are used and how the interlocking nature of American puzzles works.
Example #1: Embargoed country
Looking at the grid, you note that the answer has four letters. Thus, this could be several different answers: IRAN, IRAQ, and CUBA all fit this clue. The letter that varies in all cases is the fourth letter, which happens to also be the first letter in another clue - appliance maker - which itself has five letters. The number of appliance makers with five letters in their name is pretty small; only AMANA comes to mind immediately. Fittingly, the A to start AMANA matches up perfectly with the A ending CUBA, so we can reasonably pencil in both answers.
Example #2: Day of the week
Glancing that this clue is in fact six letters long leaves you with MONDAY, FRIDAY, and SUNDAY. We can go ahead and fill in the last three letters, but from here we have to move on to get additional letters as a clue. The first or second letter will give it away.
Example #3: Famous Met
Given the capitalization of Met, we can reasonably assume that the clue refers to the famous New York Mets baseball club. The clue has six letters, so we can likely include GOODEN, PIAZZA, CARTER, and possibly both MOOKIE and WILSON referring to the same player. If this is a New York newspaper publishing the crossword, it's likely that even more names are possible. Unquestionably, more clues will be needed to nail this one down.
Sources of Crosswords
As in the United Kingdom, most American newspapers run a daily or weekly crossword puzzle. In addition, there are many American magazines devoted to crossword puzzles and other pencil puzzles.
The New York Times produces what is generally considered to be the best regular crossword puzzle in the United States. You can try out the New York Times crossword for free at http://www.nytimes.com/pages/crosswords/index.html where a sample puzzle is provided, although to regularly play the daily and Sunday crossword you'll have to pay a subscription fee. The New York Times crossword is so highly regarded that it is often syndicated to other newspapers across the United States.
GAMES Magazine, published every other month, usually features several excellent crossword puzzles, including the traditional "World's Most Ornery Crossword," which is usually quite a challenge. GAMES usually includes a pair of British-style crossword puzzles as well, referring to them as "Cryptic Crosswords." Recently, GAMES has begun to publish a sister publication called GAMES World of Crosswords, which is loaded with a selection of excellent crosswords of varying difficulty.
Perhaps the most well-known modern crossword puzzle maker is Will Shortz, who is the editor of the New York Times crossword puzzle and a former editor of GAMES Magazine. Shortz's puzzles usually interject a level of humor and playfulness not often seen in the work of other crossword puzzle architects.
A comprehensive list of online American crossword puzzles can be found at http://www.primate.wisc.edu/people/hamel/cp.html.
Crossword Creation - Why Not Use Computers?
Given the nature of the American crossword, it is easy to see that a computer program could generate countless crossword puzzles given a large enough database of answers and clues. In fact, it is the type of task that computers excel at. However, one finds that crossword puzzles generated by computer are often quite bland, owing to the fact that the clues are just that, randomly generated. The interjection of themes into crosswords is often ham-fisted if done by computer, and thus the puzzles themselves are uninteresting.
As a result, American crossword puzzle creation is, much like many other human endeavors, an art of sorts. Shared themes among the clues, connected clues, and even more subtle elements combine to make an enjoyable crossword puzzle much more than the sum of its parts.