Old maps as visual documents are significant historical records that explain the changes within cities. However, much information has disappeared with the lack of a professor system for collections of urban maps before the 18th century. This is true of  especially coloured urban maps. This information, and the associated knowledge, could be rediscovered by analysis of these maps. Thus, it needs methods, under the umbrella of visual analysis, which focus on exploring graphic elements in visual resources. Thus, this paper will discuss one of the methods for analysing the graphic elements in historical urban maps, focusing on colour language. Using in historic maps many elements have little contextual information due to lack records and development of cities, resulting in alterations in maps. One example, is the difficulty in finding the functions, materials and owners of common buildings (e.g. houses) when compared with famous building (e.g. cathedral) in a city map. Understanding the meaning of graphic elements on historical urban maps explores symbols, without reference to text records. Thus, how to code and classify these graphic elements depends on visual analysing from primary materials. Therefore, it requires the understanding and discussion of visual content analysis to research the meanings and the hidden information of graphic elements in historical functional images, which have little other context. As there is a large amount of repeating information in an urban map, it is useful to compare and summarise the similarity, and differences, of data as systemic samples. This highlights the function of visual content analysis again.