The use of maps as a complex source of geographical information requires a certain level of mathematical literacy. The lack of such literacy can cause severe failures in map use and the development of map skills. Therefore, this paper aims to contribute to the discussion about the difficulties in using quantitative thematic maps (specifically choropleth maps and proportional symbol maps), which may result from insufficient level of mathematical literacy at the lower secondary level of education. The paper is structured into two studies: Study 1 focuses on the continuity of mathematics and geography curricula (employing methods of expert cognitive walkthrough and content analysis), while Study 2 examines the relationship between achieved mathematical literacy and map skills (using two achievements tests and a questionnaire). The findings show that the continuity of curricula often fails and that map skills development precedes the development of mathematical literacy. The identified inappropriate chronology might have important consequences, since the correlation of mathematical literacy with the level of thematic map use skills proves to be statistically significant. Their relationship is significant in all aspects of map use (map reading, analysis, and interpretation) and in the use of both types of quantitative thematic maps examined in the study. The results should be of interest to geography teachers, teacher trainers, and curriculum leaders on the national and school levels.