http://books.google.com.br/books?hl=en&lr=&id=FBURAQAAIAAJ&oi=fnd&pg=PA1&dq=Curvas+de+nivel&ots=yz5WGKi62d&sig=219EwhzS5dLt_ciAVT4x1vaw6hE#v=onepage&q=Curvas%20de%20nivel&f=false
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http://www.infoescola.com/cartografia/curva-de-nivel/

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http://geographicae.wordpress.com/2007/06/09/formas-de-relevo-e-curvas-de-nivel/