An analyzed chart of surface weather observations. Essentially, a surface chart shows the distribution of sea level pressure, including the positions of highs, lows, ridges, and troughs and the location and character of fronts and various boundaries such as drylines, outflow boundaries, sea-breeze fronts, and convergence lines. Often added to this are symbols of occurring weather phenomena, analysis of pressure tendency (isallobars), indications of the movement of pressure systems and fronts, and perhaps others, depending upon the intended use of the chart. Although the pressure is referred to mean sea level, all other elements on this chart are presented as they occur at the surface point of observation. A chart in this general form is the one commonly referred to as the weather map. When the surface chart is used in conjunction with constant-pressure charts of the upper atmosphere (e.g., in differential analysis), sea level pressure is usually converted to the height of the 1000-mb surface. The chart is then usually called the 1000-mb chart.