Herein lay his greatness and his limitation.
These facts brought the writer face to face with a serious problem.
Ratzel's work needed to be tested, verified.

The only solution was to go over the whole field from the beginning, making research for the data as from the foundation, and checking off the principles against the facts.
This was especially necessary, because it was not always obvious that Ratzel had based his inductions on sufficiently broad data; and his published work had been open to the just criticism of inadequate citation of authorities.

It was imperative, moreover, that any investigation of geographic environment for the English-speaking world should meet its public well supported both by facts and authorities, because that public had not previously known a Ritter or a Peschel.
The writer's own investigation revealed the fact that Ratzel's principles of anthropo-geography did not constitute a complete, well-proportioned system.

Some aspects of the subject had been developed exhaustively, these of course the most important; but others had been treated inadequately, others were merely a hint or an inference, and yet others were represented by an hiatus.

It became necessary, therefor, to work up certain important themes with a thoroughness commensurate with their significance, to reduce the scale of others, and to fill up certain gaps with original contributions to the science.