EVS-Islands

If you are going to digitize the outline of an island, you begin by selecting an island. This is an old project that I worked on previously. I like to work at this zoom level (1:10,000). It alllows me to fine tune my digitizing. I feel my ability to accurately interpret the image data is solid at this level. It would make sense that the closer I can get to my work the more accurate the digitizing would be. Not so! The above image clearly shows a key zoom problem - the individual pixels overpower the image they are intended to depict. Instead of seeing a picture of an island I see a picture of colored squares. If I didn't know I was working on an island shoreline, I could not guess what the underlying image was supposed to be. However, Global Mapper has an option that allows me to "interpolate" the underlying data, even at this scale. The option is Anti-Alias Pixels (Interpolate). The process smooths the pixel edges and makes a "best guess" as to what those pixels are trying to show - an island shoreline with a vegetation layer. The point of this exercise is to demonstrate that raster images (pictures) when zoomed too far become a collage of colored squares - pixels. Some smart programs, like Global Mapper, created routines that attempt to overcome this weakness. The best type of map when working at these very close zoom levels is a vector map. A vector file will show crisp clean lines at whatever scale you choose to work in. The one above is 1:6-meters. If you want a pretty map, work with pictures (raster images). If you want a practical map for a wide variety of applications and dynamic scales, work with vectors. OT: Special Topic

Posted by Mr Minton on Thursday, April 27, 2006 at 4/27/2006 12:35:00 PM | Permalink