What are the lines and numbers on a surface map?

The lines on a surface map are called isobars.

Isobars are lines of constant pressure which are measured in units called millibars.

The numbers indicate the amount of air pressure, in millibars, that each line represents.

These lines and numbers are necessary find out exactly where High and Low pressure systems are on the maps.

» More Homework Help Questions

Interactive Radars

Regional Headlines

This Week's Circulars

Regional Radar Image

Live Traffic Cameras

Cameras provided by PennDOT

Historical Averages

High Low
Current 68°F 54°F
Average 64°F 41°F
Record 93°F April 26, 1915 30°F April 26, 2001