In 1877-1881, he executed a topographic and geological survey of 17,000 square miles (44,030 km2) in northeastern Iowa.
Co-ordinates, elevation and distances given according to a 1995-96 Bulgarian topographic survey.
Bulgarian topographic survey Tangra 2004/05 and mapping in 2005 and 2009.
M. North conducted a topographic surveys by 1955.
The term "topographic surveys" appears to be American in origin.
He made topographic surveys to compare different options in 1843 at his own expense.
The peak was mapped by Bulgaria from a 1995-96 topographic survey.
On December 8, three workers started a topographic survey of what would become Ault Field, about four miles to the north.
Bulgarian topographic survey in 1995/96, and mapping in 2005 and 2009.
He had scouted out his target in advance, with some assistance from surveillance satellites and topographic surveys.
