A geographical map viewer is a software application or online tool that allows users to interact with and view maps on a digital device, such as a computer, tablet, or smartphone. These map viewers provide a user-friendly interface for exploring and navigating geographic information.

Here are some key features and functions typically associated with geographical map viewers:

1. Map Display
The primary function is to display maps. Users can view maps of specific regions, countries, cities, or even detailed street-level maps, depending on the viewer's capabilities.

2. Zoom and Pan
Users can zoom in to see more detailed information or zoom out to get a broader view. Panning allows users to move around the map to explore different areas.

3. Layer Control
Many map viewers support multiple layers of information. Users can toggle on or off various layers, such as roads, satellite imagery, terrain, or other thematic layers, to customize the displayed information.

4. Search and Location Services
Users can search for specific locations or addresses. Map viewers often provide tools to locate and highlight points of interest or find directions between different locations.

5. Geospatial Data Integration
Some map viewers allow users to integrate additional geospatial data layers, enabling the overlay of information like population density, land use, weather patterns, etc.

6. Annotations and Markers
Users can add markers and annotations or draw on the map to highlight specific areas or points. This is useful for planning, analysis, or marking points of interest.

7. Measurement Tools
Map viewers often include tools for measuring distances, areas, or other spatial dimensions directly on the map.

8. Responsive Design
Many modern map viewers are designed to be responsive, adapting to different screen sizes and devices, providing a seamless experience across desktop and mobile platforms.

9. Sharing and Collaboration
Some map viewers allow users to share their maps or collaborate with others by providing links or embedding maps in websites or applications.

10. Real-time Data and Updates
In some cases, map viewers can display real-time data, such as traffic conditions, weather updates, or other dynamic information.

Famous examples of geographical map viewers include Google Maps, Bing Maps, OpenStreetMap, and various GIS (Geographic Information System) applications. These tools play a crucial role in helping individuals, businesses, and organizations explore, analyze, and understand spatial information.