The integration of digital maps and geographical information into Geographical Information Systems (GIS) produces solutions for several groups of users. There is an increasing number of non experts that use GIS on the Web or in desktop applications to locate addresses, plan routes and trips, find places, and so on. Less complex applications designed for general use critically need evaluation, because their commercial success depends heavily on the quality of human-computer interaction. In spite of such critical need, it is very hard to find research about how to evaluate these kinds of simpler applications. We propose a semiotic inspection method (whose acronym in Portuguese is ISIM) that analyzes the effect of representations in map-based interfaces to communicate geographic information. ISIM combines analytic and empirical techniques to carry out evaluations. Analytic techniques are used to define contexts of use and users' profiles, as well as to interpret empirical observations. ISIM also uses an empirical technique of tests and interviews with users. ISIM, whose scope encompasses only GIS map-based interaction, can identify a class of basic problems of interaction and, as is the case with many semiotic methods, hint at design solutions for them.