Content such as maps, charts, and diagrams can be very difficult to describe concisely while still providing relevant information.
If the information conveyed by the map is covered within the text of the webpage then alt text that says "map of waste collection route" might suffice. You can also include GPS coordinates as many assistive technology users are familiar with using GPS. Alternatively, you can describe the route, for example, "Map of waste collection route. Start at the intersection of Mountain and Sky streets. Make the second right onto Fall Avenue...". The main thing to remember is that the context of the map must be considered. It’s not always necessary to describe the entire map.
For graphs and charts, we would recommend including a data table for any chart or graph within the page. If that isn’t possible, either general trends should be described, or each data point should be described in the alt text (depending on how complex the chart is). You can use alt text like this for the graph or map images, e.g. "Chart showing a downward trend over 5 years; refer to the data table on this page for specific details."