Why is the graph method of finding area not considered 100% accurate?

Isobars are lines of constant or equal pressure on a weather map. they can be used to find areas of low or high pressure over a broad area, and they can tell us how intense the system may be. on weather maps, you may have noticed areas that have a large l or h over a region with lines circling around them. the l stands for low pressure and h stands for high pressure. the lines circling them are isobars. check out the pressure system and isobars over georgia and florida. what is the present weather in this area ? a) clear and sunny b) cold and cloudy c) changing weather d) lots of precipitation