Which conclusion is most clearly supported by the information in the map? the belief in laissez-faire prevented the federal government from railroads. the federal government promoted transcontinental railroad construction. western railroads generated little profit for their owners. railroad companies had to buy the land they needed for construction?

Even without the map, we can assert this:  The federal government promoted transcontinental railroad construction.

Railroads were given land grants by the federal government, which not only provided land for the railroad itself, but the companies were able to sell some parcels of the granted land to help finance railroad construction.   The railroad companies also received government bonds for completing certain amounts of track miles across the plains.  Provisions like these were in the Pacific Railroad Acts of 1862 and 1864.