How do you get a paper map into your GIS?
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In previous videos I’ve spoken about points, lines and polygons, and where you get GIS data from. Today I want to talk about how you get vector points, lines, and area (polygon) features from a paper map into a GIS. Its important stuff because a GIS without maps is just a piece of software!
Paper maps are converted to GIS maps through a process called digitizing. As I pointed out in a previous video, a paper map might also be a map that you’ve interpreted yourself. You need to know up-front that digitizing is a pain. Its fiddly, frustrating and time consuming. Its also necessary and rarely is the effort not worth it. As a GIS professional, if you think you can avoid digitizing then you’re either working in a well kitted-out organization with a completed GIS database, or you’re lazy. Too often I see “lazy” and it just frustrates me!
There are two broad approaches to digitizing. The first involves using a digitizing tablet and the second an image scanner. Today I'm going to show you how to use a digitizer.
Tablet digitizing involves the use of a digitizing tablet and cursor tool called a "puck", which, simplistically is a highly accurate mouse with locator cross-hairs behind a magnifying lens. You mount your paper map on the digitizing tablet using removable sticky-tape, and then trace the cross hair axis along each feature on the paper map – click-click-click. The puck movement is detected by the fine mesh of wires inside the tablet and each “click” (or movement) is captured as a feature coordinate.
An advantage of this approach is that map features can be easily recorded as map layers. For example, a paper map with road and water features could be digitized into a map of roads, a map of rivers and a map of water bodies. The work is time-consuming labor intensive and prone to error. Whoever is doing the digitizing needs to be methodical and have a steady hand. There are a whole bunch of validation procedures that government mapping agencies use when taking this approach.
Next video: Getting a paper map into your GIS using a scanner.ont forget to signup for my FREE eBook if you haven't already!!!
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