Drupal is an amazing tool for mapping. It integrates with a lot of libraries, technologies and third party services. There are solutions for simple maps but also for complex mapping needs.
On mapping there isn't one ideal solution, because it depends of the project. Although, there is always a path: input > storage > process > output, some modules may provide more than one of these steps.
If you start mapping with Drupal, you almost likely use a combination of modules to achieve your goal. The documentation section contains a description of main modules to help you on your selection.
Widely used approaches
There are several approaches:
- Location (D6, D7) & Gmap (D6, D7)
- Geofield & OpenLayers or Leaflet (all D7)
- Get Locations (Google Maps v3 solution for D6, D7), either by itself or with Geofield (D7) or Geolocation field (D7)
- one of Location, Geofield, Geolocation field, Get Locations or other contrib module in combination with the IP Geolocation Views and Maps rendering engine (all D7). Supports Google Maps v3 directly, as well as Leaflet and OpenLayers.
Which one to pick depends on the nature of the project (e.g the location data storage modules you may be committed to) and the skill of the level you have on each technology. OpenLayers supports a number of map providers (including Google Maps), so gives you a lot of flexibility. However this comes at the expense of more complexity in configuration.
Geofield is currently the standard for storing geo data. It can be used as a stand alone solution for simple projects as it provides the input (unlike Location, it accepts points, lines, polygons), storage and display (when used with Views). But if you want more complex displays, it can be integrated with Geocoder, or libraries like Openlayers and Leaflet.
If your geographical data can be captured as a Views table, which is almost always the case, then IP Geolocation Views and Maps is a very versatile solution, connecting your choice from any of the main geo storage modules to your choice of one of the three map rendering packages (Google, OpenLayers and Leaflet). This allows you to pick and mix as you please without lock-in.
Drupal 6 vs. 7
As can be seen from the list above there are differences on the available modules for Drupal 6 and Drupal 7. On one hand because the technology is outdated, on the other because more flexible solutions appeared. Web mapping is an area that is in constant movement.