The contour interval of a contour map is the difference in elevation between successive contour lines. More generally, a contour line for a function of two variables is a curve connecting points where the function has the same particular value. The gradient of the function is always perpendicular to the contour lines.
Public finance is the study of the role of the government in the economy. It is the branch of economics which assesses the government revenue and government expenditure of the public authorities and the adjustment of one or the other to achieve desirable effects and avoid undesirable ones.
The federal government is the nation's largest borrower. By investing in U.S. Government securities, you are lending money to help finance operations of the federal government. These securities are among the highest-quality investments available, as they are backed by the full faith and credit of the government.