Scale factor and image resolution: some cartographic considerations
AbstractThe preservation of our cartographic heritage has long advocated the transformation of historical maps or, more generally, of paper maps produced by analogue methods into digital format. The development of GIS techniques and cartographic databases has allowed increasingly rapid georeferencing of scanned maps into global datums like WGS84. The prerequisite for good georeferencing is, however, good digital transformation of the paper map format. This is of course a technical issue, but it also has some mapping implications connected to cartographic generalization theory.The subject of this paper is to connect the well-recognized cartographic generalization concept (the graphicism error) to the resolution of the scanned image (measured in SPI). After a short introduction on some technical features linked to the scanning process (DPI, PPI, SPI), the scale factor of a map is briefly recalled. Then the numerical relation between the scanning resolution and the scale of the paper map is given. Awareness of this relation is useful to avoid scanner accuracy superseding the accuracy of the scanned map.
Dodge M., Kitchin R., Perkins C., “Introductory Essay: Technologies of mapping”, in Dodge M., Kitchin R. and Perkins C. (Eds.), The map reader, Chichester, Wiley-Blackwell, 2011.
Favretto A., “Georeferencing Historical Cartography: a Quality-Control Method”, Cartographica, 47:3, 2012 .
Favretto A., Strumenti per l’analisi geografica GIS e Telerilevamento, Bologna, Patron Editore, 2006 (2a Edizione).
Gartner G., “Applying Web Mapping 2.0 to Cartographic Heritage”, e-Perimetron, 4(4), 2009.
Goodchild M. F., “Citizens as sensors: the world of volunteered geography”, GeoJournal, 69, 2007.
Iliffe J. C., Datums and Map Projections. For Remote Sensing, GIS and Surveying, New York, Whittles Publishing, 2000.
Monmonier M., How to Lie with Maps, University Chicago Press, 1996.
Robinson A. H., Morrison J. L., Muehrcke P. C., Kimerling A. J., Guptill S. C., Elements of Cartography, New York, Wiley, 1995.
Tobler W. R., “Automation and Cartography”, The Geographical Review 49(4), 1959.
The Author assigns to the Nuova Cultura and to Italian Association of Geography Teachers all rights under copyright that can exist in and to the submitted paper. The Author warrants that the paper and images (photos, maps, graphs etc.) are original and that he/she is the Author of the submitted contribution and its parts; in the case of images taken by other publications, the Author must provide a specific authorization and must pay in advance any copyright.
This work is licensed under a Creative Commons Attribution 4.0 International License.