Isobaric Map

http://ruc.noaa.gov/gif/topo-ruc13.gif

http://images.google.com/imgres?imgurl=http://ruc.noaa.gov/gif/topo-ruc13.gif&imgrefurl=http://ruc.noaa.gov/&usg=__vxwnfG5EGte7iLnn7J-itzhL_xQ=&h=1000&w=1000&sz=109&hl=en&start=8&um=1&itbs=1&tbnid=f0eFlynkjKRekM:&tbnh=149&tbnw=149&prev=/images%3Fq%3Disobaric%2Bmap%26um%3D1%26hl%3Den%26client%3Dfirefox-a%26sa%3DN%26rls%3Dorg.mozilla:en-US:official%26tbs%3Disch:1

Isobaric maps display air pressure. In this map you can use the scale at the bottom to determine that the highest air pressure is on the northwest side from Alaska through California and on through Mexico.