A weather map is a tool use to display information quickly showing the analysis of various meteorological quantities at various levels of the atmosphere. Maps using isotherms show temperature gradients, which can help locate weather fronts. Isotach maps, analyzing lines of equal wind speed, on a constant pressure surface of 300 mb or 250 mb show where the jet stream is located. Two-dimensional streamlines based on wind speeds at various levels show areas of convergence and divergence in the wind field, which are helpful in determining the location of features within the wind pattern. A popular type of surface weather map is the surface weather analysis, which plots isobars to depict areas of high pressure and low pressure. Special weather maps in aviation show areas of icing and turbulence.