> someone who is illiterate implicitly know that "1" and "0" represent People are usually OK with small numbers. So: 1 - there is a thing. 0 - there isn't a

> someone who is illiterate implicitly know that "1" and "0" represent People are usually OK with small numbers. So: 1 - there is a thing. 0 - there isn't a thing. (I know that you went with 'O' and '.' for "city" and "no-city",[and it worked nicely, thank you,] but come on ... ;-)