This study is about basic cartographic conception like sign and symbol and their vertical and horizontal connection and condition. Also, the function that they have is marked by nominal, ordinal and interval-ratio scales of measurement, i.e. levels of representing signs. All these factors are connected and give us information about qualitative and quantitative characteristics of occurrences in space that we are mapping. Beside main concept, the statistical unit for determination the key of signs for thematic maps will be also presented here. This unit gives the main characteristics of sign, which is mapped at specific map or plan. .