How do I link to Google Maps with a particular longitude and latitude?

Solution 1:

The best way is to use q parameter so that it displays the map with the point marked. eg.:

https://maps.google.com/?q=<lat>,<lng>

This schema has changed again (23rd October 2018). See Kushagr's answer for the latest.

This for a map with the marker (via aaronm's comment):

~~https://www.google.com/maps/?q=-15.623037,18.388672~~

For an older example (no marker on this one):

~~https://www.google.com/maps/preview/@-15.623037,18.388672,8z~~

The oldest format:

~~http://maps.google.com/maps?ll=-15.623037,18.388672&spn=65.61535,79.013672~~