@article{Dijkstra1959,
  title   = {{A note on two problems in connexion with graphs}},
  author  = {E. W. Dijkstra},
  journal = {Numerische Mathematik},
  volume  = {1},
  number  = {1},
  pages   = {269–271},
  year    = {1959}
}
@techreport{Tobler1993,
  author      = {Waldo Tobler},
  title       = {{Three Presentations on Geographical Analysis and Modeling: Non- Isotropic Geographic Modeling, Speculations on the Geometry of Geography, Global Spatial Analysis}},
  year        = {1993},
  number      = {93-1},
  institution = {{National Center for Geographic Information and Analysis}},
  type        = {Technical Report}
}