at a size and scale convenient for navigation by moderate speed  aircraft. They are produced at a scale of 1:1,000,000 (1 inch =  13.7 NM or approximately 16 SM). These charts are similar to  sectional charts, and the symbols are the same except there is  less detail due to the smaller scale.  [Figure 16-3]  These charts  are revised annually except several Alaskan charts and the  Mexican/Caribbean charts, which are revised every 2 years.  The equator is an imaginary circle equidistant from the poles  of the Earth. Circles parallel to the equator (lines running east  and west) are parallels of latitude. They are used to measure  degrees of latitude north (N) or south (S) of the equator. The  angular distance from the equator to the pole is one-fourth  of a circle or 90°. The 48 conterminous states of the United  States are located between 25° and 49° N latitude. The arrows  in  Figure 16-4  labeled “Latitude” point to lines of latitude.  Meridians of longitude are drawn from the North Pole to the  South Pole and are at right angles to the Equator. The “Prime  Meridian,” which passes through Greenwich, England, is  used as the zero line from which measurements are made in  degrees east (E) and west (W) to 180°. The 48 conterminous  states of the United States are between 67° and 125° W  longitude. The arrows in  Figure 16-4  labeled “Longitude”  point to lines of longitude.  Any specific geographical point can be located by reference  to its longitude and latitude. Washington, D.C., for example,  is approximately 39° N latitude, 77° W longitude. Chicago  is approximately 42° N latitude, 88° W longitude.  The meridians are also useful for designating time zones. A  day is defined as the time required for the Earth to make one  complete rotation of 360°. Since the day is divided into 24  hours, the Earth revolves at the rate of 15° an hour. Noon is  the time when the sun is directly above a meridian; to the  west of that meridian is morning, to the east is afternoon.  Time Zones  Latitude and Longitude (Meridians and  Parallels)  Figure 16-2.  VFR Terminal Area Chart and legend.  16-3 