Contour line future weather patterns. Isobars are commonly used in television weather reporting. Isallobars are lines joining points of equal pressure change during a specific time interval. These can be divided into "anallobars", lines joining points of equal pressure increase during a specific time interval, and "katallobars", lines joining points of equal pressure decrease. In general, weather systems move along an axis joining high and low isallobaric centers. Isallobaric gradients are important components of the wind as they increase or decrease the geostrophic wind. An isopycnal is a line of constant density. An "isoheight" or "isohypse" is a line of constant geopotential
Nautical chart great circle routes. NOAA uses the polyconic projection for some of its charts of the Great Lakes, at both large and small scales. Positions of places shown on the chart can be measured from the longitude and latitude scales on the borders of the chart, relative to a geodetic datum such as WGS 84. A bearing is the angle between the line joining the two points of interest and the line from one of the points to the north, such as a ship's course or a compass reading to a landmark. On nautical charts, the top of the chart is