As a part of the development of the Italian Cartographic Reference System, the Italian Ministry of the Environment has developed, in collaboration with Planetek Italia, a public web site (www.atlanteitaliano.it), allowing unrestricted Internet access to various types of maps and photographic images covering the whole of Italy. The types of data available online include black and white and colour orthophotos at 1 meter resolution (nominal scale 1:10,000); maps of the Italian Geographic Military institute (IGM, scale 1:25,000, 1:100,000, 1:250,000 1:1,000,000); and a digital elevation model (DEM). The data, compressed in ECW format, are distributed using Image Web Server with the specific advantage that the imagery may be accessed via the Internet in real time in two ways; either through the website using a common browser or directly inside any common supported desktop GIS application using the individual image URL (only registered and entitled users are permitted access to the URLs). By going to the web site, users are given three different ways to view the cartography: single view, double view and transparency.
Transparency: this kind of visualization allows the overlaying of two different images with full, on-the-fly, transparency and layer position control. Viewing images in this fashion permits different kinds of visualization, for example, multi-temporal analysis can be carried out between data acquired in different years, for the monitoring of environmental change. The images need not be the same type, thus you can overlay and compare recent orthophotos with older cartographic data. Using ER Mapper, the thousands of individual images were all mosaiced together into single images, one for each data type for a specific region. After mosaicing, the images were colour balanced and then directly compressed into ECW format. This format produces a dramatic reduction in the size of the image files and permits the high speed serving of the data by Image Web Server.