Looked at in one way, there is no such thing as an isobar. You cannot see it or feel it, or come across it in any tangible form in real life. It exists only in the imagination, a theoretical concept introduced as a mental crutch, to help assemble thousands of values of atmospheric pressure into some form of recognisable pattern.
In this context, the isobar is very different from a front. A front is equally prominent on the weather map you see each evening on the television, but it has a real existence as a boundary between two masses of air, and its physical presence out of doors is often marked by clouds and heavy rain.
Isobars, you will recall, are the lines on a weather chart drawn through points of equal barometric pressure. They resemble in some ways the contour lines used by cartographers, who draw lines on a conventional map joining points which are the same distance above sea level.
Indeed, a finished weather chart is closely analogous to a map of the physical features of a given area - except that instead of mountains and valleys and other ups and downs of the terrain, the isobars identify areas of high and low pressure - anticyclones and depressions. Moreover, by looking at an Ordnance Survey map, the practised eye might judge the direction in which a ball, placed at a certain spot, might roll - and make a guess as to how rapidly it would proceed downhill. In much the same way, isobars tell the weather forecaster the likely speed and direction of the wind.
The wind direction at any point on the chart coincides, more or less, with the direction of the isobars; it flows along them with low pressure to the left - which, if you work it out, means that it blows anti-clock- wise around an area of low pressure. In addition, the speed of the wind is inversely proportional to the distance apart of the isobars; the closer they are together, the stronger the wind will be.
On maps covering a large area, isobars are normally drawn at four hectopascal intervals - as indeed they are on the main weather chart on this page. Since each line represents a specific value of pressure, isobars never cross; if they did, it would imply two different pressure values at the same point - which is clearly an impossibility. And an isobar never ends, except at the very edge of a chart; indeed if isobars were drawn on the globe, each and every one of them would be a continuous closed curve , returning ultimately to the very point where it began.