11 FAA Chart Users’ Guide - VFR Terms and Symbols EXPLANATION OF VFR TERMS AND SYMBOLS WATER FEATURES (HYDROGRAPHY) LAND FEATURES (TERRAIN) AND OBSTRUCTIONS 2.  Shaded relief shows how terrain may appear from the air. Shadows are shown as if light is coming from the northwest, because studies have shown that our visual perception has  been conditioned to this view.  1.  Contour lines join points of equal elevation. On Sectionals, basic contours are spaced at  500' intervals. Intermediate contours are typically at 250' intervals in moderately level or  gently rolling areas. Auxiliary contours at 50', 100', 125', or 150' intervals occasionally  show smaller relief features in areas of relatively low relief. The pattern of these lines  and their spacing gives the pilot a visual concept of the terrain. Widely spaced contours represent gentle slopes,  while closely spaced contours represent steep slopes.  The elevation and configuration of the Earth's surface is important to pilots. Our Aeronautical Information Specialists are  devoted to showing the contour of the earth and any obstructions clearly and accurately on our charts. We use five differ - ent techniques: contour lines, shaded relief, color tints, obstruction symbols, and Maximum Elevation Figures (MEF). Exceptionally large lakes like the Great Lakes, Great Salt Lake, and Lake Okeechobee, etc., are considered Open Water  features. The Open Water tone extends inland as far as necessary to adjoin the darker blue "Inland Water" tones. All other  bodies of water are marked as "Inland Water" in the darker blue tone. Water features are depicted using two tones of blue, and are considered either "Open Water" or  "Inland Water." "Open Water," a lighter blue tone, shows the shoreline limitations of all coastal water  features at the average (mean) high water levels for oceans and seas. Light blue also represents the  connecting waters like bays, gulfs, sounds and large estuaries. Aeronautical Information Services' charts are prepared in accordance with specifications of the Interagency Air Committee  (IAC) and are approved by representatives of the Federal Aviation Administration (FAA) and the Department of Defense  (DoD). A brief description next to a small black square indicates the exact location for many of the landmarks easily recognized  from the air, such as stadiums, pumping stations, refineries, etc. A small black open circle with descriptive type indicates  oil, gas or mineral wells. A small black circle with descriptive type indicates water, oil or gas tanks. The scale for some  items may be increased to make them easier to read on the chart. The chart legend includes aeronautical symbols and information about drainage, terrain, the contour of the land, and  elevation. You can learn to identify aeronautical, topographical, and obstruction symbols (such as radio and television tow- ers) by using the legend. This chapter covers the Sectional Aeronautical Chart (Sectional). These charts include the most current data at a scale  of (1:500,000) which is large enough to be read easily by pilots flying by sight under Visual Flight Rules. Sectionals are  named after a major city within its area of coverage.