What information might the geographer be able to convey more clearly than the economic historian

Since a geographer is the scientist whose field of study is geography, the study of Earth's natural environment as well as human society, an information that a geographer might be able to convey more clearly than the economic historian would be the patterns of how human beings migrated over time as a result of the climate change and environment which made them to move. 

On the other hand, economic historians are responsible with the study of economies or economic phenomena of the past.

in 1803 the louisiana purchase took place, doubling the size of the country. by 1840 almost 7 million americans had migrated westward in hopes of securing land and being prosperous. the belief that settlers were destined to expand to the west is often referred to as manifest destiny.

explanation:

new evidence is discovered.

oversights and errors are corrected,

new technology is applied to evidence.