This PhD research work is placed in the domain of Geovisualization used to implement Territorial Intelligence and decision support systems. This research work was born through the establishment of an agreement between Tor Vergata University, Rome, and INSA (Institut National des Sciences Appliquées), Lyon. The co-supervision of this thesis was born from the necessity of a multidisciplinary approach to the research topic, taking advantage of the skills in urban planning, environment and territory modeling at the Geoinformation doctoral school of Tor Vergata University, and taking advantage of the skills in Spatial Information Systems and Geovisualization at the LIRIS Laboratory of INSA. The motivation that led us to deal with this research topic was the perception of a lack of systematic methods and universally approved empirical experiments in data visualization domain. The experiments should consider different typologies of data, different environmental contexts, different indicators and methods of representations, etc., in order to support expert users in decision making, in the urban and territorial planning and in the implementation of environmental policies. In modern societies, we have to deal with a great amount of data every day and Geovisualization permits the management, exploration and display of big and heterogeneous data in an interactive way that facilitates decision making processes. Geovisualization gives the opportunity to the user to change the visual appearance of the maps, to explore different layers of data and to highlight problems in some areas by the citizens. Despite these advantages, one of the most common problems in Information Visualization is to represent data in a clear and comprehensible way. Spatial data have a complex structure that includes spatial component, thematic attributes, and often the temporal component Actually there are limited scientific foundations to guide researchers in visual design of spatial data, and there are limited systematic and standard methods to evaluate the effectiveness of the solutions proposed. In this Phd research work, some contributions will be provided to the creation of a systematic assessment method to evaluate and to develop effective geovisualization displays. An empirical evaluation test is proposed to assess the effectiveness of some map displays, analyzing the use of three elements of visual design: 1. the spatial indicators to be represented and their context of visualization, 2. the physical dimensions of map displays, 3. the visual variables to represent different layers of information.