Links
[1] https://www.e-education.psu.edu/egee401/instructor
[2] http://esp.e-education.psu.edu/
[3] https://esp.e-education.psu.edu/node/947
[4] http://www.libraries.psu.edu/psul/researchguides/geoearthsci/geography.html
[5] https://www.e-education.psu.edu/egee401/node/1761
[6] https://www.e-education.psu.edu/egee401/p5.html