  Geovisualizations are powerful tools for exploratory spatial analysis,
enabling sighted users to discern patterns, trends, and relationships within
geographic data. However, these visual tools have remained largely inaccessible
to screen-reader users. We present AltGeoViz, a new system we designed to
facilitate geovisualization exploration for these users. AltGeoViz dynamically
generates alt-text descriptions based on the user's current map view, providing
summaries of spatial patterns and descriptive statistics. In a study of five
screen-reader users, we found that AltGeoViz enabled them to interact with
geovisualizations in previously infeasible ways. Participants demonstrated a
clear understanding of data summaries and their location context, and they
could synthesize spatial understandings of their explorations. Moreover, we
identified key areas for improvement, such as the addition of intuitive spatial
navigation controls and comparative analysis features.
