Well, here's another in my subscriber-only series of posts. Please feel free to share it with your Twitter or Facebook friends. They'll get the most benefit from it if they download the FREE eBook though. Unless they do that they wont find out about other new posts in this series.
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!!!
PLEASE GIVE ME FEEDBACK: This is a young site and I'd like to make it relevant to people wanting to learn GIS. My thoughts are that I'll start with a few examples of GIS applications, mostly from the eBook before going into detail about GIS theory. I'd really like your feedback about what you want. For example is this video too long for you & would you prefer it to be split up? Or do you just want to know about the GIS techo stuff? Please write you comments below. I make use of the Facebook commenting system - it is a way to ensure less spam on the site.