It is well-known that, when dealing with density of population, most of the proposed maps choose the easiest and probably the most understandable cartographic method, i.e. the choropleth method. Nevertheless, for heterogonous spaces and those observing intense spatial dynamic, it is proven that this method has many lacks and deficiencies. This is the case of Jeddah city (the second largest city in Saudi Arabia), which is a very contrasted urban place with regards to its social structure, spatial organization and land use besides the fact that it witnesses a profound and continuous urban growth. Yet, most of the planning decisions are often taken on these types of maps and may mislead the urban planners. In this context, the dasymetric maps reveal very useful because they may give the real distribution of the population. Therefore, we think that establishing a dasymetric map at a convenient scale with regards to the results of satellite image processing may help the planners and the geographers as well as the common users. Indeed, this method may be an interesting alternative to the classic choropleth map. First it may improve our estimations towards the density within the various areas of the districts. Second it may refine the original enumeration units often using the administrative apportionment and therefore help the planning and agricultural agencies when establishing their base maps. The satellite image processing and GIS were used as tools in this study.

No abstract

The "Technological Transition" has had a tremendous impact on cartographic processes and outputs. Atlases, whether national, regional or urban, were affected as they moved from a static to an animated and interactive era. The overall positive development, consolidated by map automation and map animation, has taken various forms and directions. Nevertheless, some graphic and cartographic outputs, especially atlases, still suffer from serious pitfalls, regarding some semiological aspects of the resulting maps and graphics. The Digital Urban Atlas of Jeddah (DUAJ) is a research in progress aware of such deficiencies. It tries to spare it from some frequent errors in map design related to: the choice of the base map, the use of some frequent symbols such as columns and pie charts for multivariate quantitative data, and the alternative solutions to choropleth maps. These deficiencies are selected and examined among others. The authors are convinced that the generated maps and diagrams that should be produced in digital atlases must be examined with regards to the semiological rules that drew upon the theory of signs perception. They try to incorporate the basic principles of graphic semiology reviewed, corrected and adapted to the GIS requirements. This is also meant to avoid map noises and deficiencies. The goal is to attract future Digital Atlases producers towards developing higher interest in map look and design and users to grasp messages rapidly. Specifically, the use of GIS and linked spatial databases within the DUAJ should not pay attention only to data handling and crossing, but also, to the semiological features of the outputs and relevant visual communication. In its preliminary stage, the DUAJ should give answers not only to the three questions raised in this research but also to others not examined here. This is to prevent from incorrect, irrelevant or inadequate use of the cartographic tools and, following the analysis of concrete examples, to propose a set of recommendations in establishing maps and graphics. When necessary, the DUAJ GIS-based outputs are inserted in CAD or CAC systems to benefit from some their specific visual tricks and subtleties that yield better legibility and efficiency of communication for Atlases users as How to cite this paper:

No abstract