This service uses a variety of digital terrain models (DTM) and digital surface models (DSM) to provide global coverage up to 60N and accuracy of up to 1 metre. If you want to add your own LIDAR see here.
Global coverage up to 60N is provided by Shuttle Radar Topography Mission, version 2, data from NASA. It was created in 2000 and has a resolution of 90m.
For the USA a higher resolution version of SRTM2 is available. It was created in 2000 and has a resolution of 30m.
Global coverage up to 60N is provided by ALOS global digital surface model © JAXA. It was created in 2014 and has a resolution of 30m.
High altitude regions such as Greenland, Northern Norway and the Svalbard islands have been created at 90m resolution from mapping by Jonathan de Ferranti http://viewfinderpanoramas.org/
High resolution tiles mapped by plane and drone have resolutions ranging from 1-8m and are added for select areas. Currently UK, New York, Los Angeles, San Francisco, San Diego, Washington DC, Philadelhia, Baltimore, Syndney, Brisbane, Westcoast Australia, Christchurch NZ, Nepal
NZ 8m DTM
Sourced from LINZ. CC-BY 3.0. http://www.linz.govt.nz/data/licensing-and-using-data/attributing-elevation-or-aerial-imagery-data