In the 1960s, the notion of accessibility was enlarged by the concept of impedance. This type of resistance could be represented by distance or by time or costs. Thanks to the modern information technologies the usage of the shortest distance method is easier nowadays. However, the human element is still necessary. The main problem is time-space transformation and the necessary network-analysis software. Time-space transformation is in fact an exchange of distance values for specific time duration. In the case of public transport, the solution is easy because of time schedules. Nevertheless, expert estimation is needed for individual car transportation and for building up a model. Time-space transformation is part of some software applications as route planners. Methodology for creating an accessibility model: it is necessary to develop digital model of road network. The main problem of all digital data is that they are too recent. Therefore, we had to convert to digital form an analogue road atlas from 1991. On the other hand, many digital geographic data were available for 2001. There are many criteria for road categorization: type of road, number of lanes, slope, location in built-up area and others. Particularly slope analysis was a very complicated geoinformatic task. Powerful hardware is also needed. However, a higher GIS literacy is necessary for instance for slope analysis. We used the software ArcGIS, version 9.2. with extensions: Network analyst and 3D analyst. A 3-dimensional terrain model was created to deduce altitude. Each starting and ending point of all road and motorway segments was assigned exact elevation. Then horizontal slope was calculated. The analysis was performed for both time periods (1991 and 2001). The most important part of the model creation consists in the discussion of average speed on roads. There are many factors that play a role in increasing and decreasing average speed. The best way to determine the most exact values is to use several methods: field research, research in relevant literature and articles, use of route planners. The obtained values were then processed by comparative analysis and subjected to logical evaluation. Two digital models of Czechia were created for the 1991 and 2001 censi years. They will be the base for further geographical analysis of transformation in Czechia, for instance for finding periphery areas. Two isochronic maps are enclosed to demonstrate functionality of the two models. The models clearly show that accessibility improved during the transformation: in 2001, it decreased by more than one hour between Prague and Ostrava. Thus, the accessibility of Prague was two and a hours, except from the eastern Moravia. The analysis is valid only for car transport. Nevertheless, in 2001 there were several railway corridors. The highest insufficiency of the models is in their accuracy. However, we have used several methods to determine the average speed. The only way of making the model and the average speed values more exact is to make a field trip in cars with GPS locators. Other factors influencing accessibility could also be included into the analysis, as car flow or road diversions. These could be subject of our following research. Fig. 1 - Selected factors influencing the average speed on roads. In columns from left: road type, within/without built-up areas, state of road and reparations, time of the day, width of the rod, average speed, state of vehicles, lengthwise inclination of the road, traffic intensity, accident frequency, season. Source: author's investigation. Fig. 2 - Isochrones of time accessibility of Prague in (above) and 2001 (below). White - more than 240 minutes or not analysed. Line - motorways, fast roads, road of 1st and 2nd category.
