I have used National Geographics World Basemap as a backgroud for several maps in my thesis. How to cite this source in a list of references? (e.g. National Geographics World Basemap, (2011), ????? accessed on .....). Can it be abbreviated as, for example "NGWBM" ?
Thanks for a tip! So, the actual reference will look like this (?):
National Geographic, Esri, DeLorme, NAVTEQ, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, iPC, (2011). National Geographic World Map, digital topographic basemap of the world. Accessed on-line http://www.arcgis.com/home/item.html?id=b9b1b422198944fbbd5250b3241691b6 on 27.03.2012.
and the reference in a text shall be (National Geographic et al., 2011) (?).
In fact it's a good idea to provide the "How to cite" section to the basemap descriptions so people can know for sure how to reference these maps in their work; ArcGIS on-line services are becoming more and more popular each year.