Scale Changes with Digital Data

All digital map data has a scale at which it was digitized, and at which it faithfully shows features. This scale provides a tradeoff between (1) excessive data storage requirements, and processing time to display and manipulate the data, and (2) accurate representation of the data.  There are times when you want to see the forest, and other times you want to see the trees, and a single data set might not efficiently accomplish both requirements.

More detail with raster data means smaller pixels, and more of them.  The more pixels goes up with the square of the improved resolution (1 m data requires 100 times more pixels than 10 m data).

Blowing up or zooming out with Raster Data:

• To blow up (move to larger scale) raster data, each pixel will be displayed multiple times. With enough blow up the pixels become very large, blocky, and distracting.  With a DEM, the software can mask this effect by interpolating elevations, but the result will be a very smooth surface that does not show the detail that should really be present.
• To zoom out (move to smaller scale) with raster data, some pixels are not shown. Data disappears.

More detail with vector data means more points to define the lines, with the points closer together.

Blowing up or zooming out with Vector Data:

• To blow up vector data, the individual points plot farther apart and the straight line segments become very noticeable.
• To zoom out with vector data, many individual points plot on the same pixel on the screen, and it takes a long time to plot. The screen might also become a solid mass of fused lines, with only the last lines drawn visible. Zoomed out data might reduce the number of categories it attempts to show.

Last revision 8/20/2019