How To Find The Distance Betwen Two Longitude Lines At A Known Latitude?

Basically there are different distances between longitudinal lines. The reason is that longitudinal lines can vary, depending upon their different latitudes. When the latitude of two longitudinal lines will increase then their distance will lessen. For example, when the latitude is known and it is 30 degree then there will be 69.171 statute miles difference between the longitudinal lines at the equator. On the other hand, at this latitude there will be 59.956 statute miles distance between the lines. When the latitude will be doubled and becomes 60 degree then distance will be 34.697 statute miles. In this way the distance is calculated by making comparisons of different values of latitudes. You can also get it from the world maps.