There are two basic types of data when it comes to GIS: vectors and rasters.
Vectors are any kind of shapes that involve points, lines, or polygons. Attribute tables that are associated with vector files often have one row of data for each object. Five settlements? This means five points or five shapes (outlining the settlements) and five rows in the attribute table. A hundred road segments? This means 100 lines and 100 rows of data. You get the idea!
Raster files are made up of many, many tiny squares, each of which contains a value of some kind. Photographs are a kind of raster file – if you zoom in far enough, you can start to see the individual pixels that make up the image. And at the data level, each pixel in the photograph has a color value that tells the computer which color to display. The same thing is happening when you look at a raster that codes for elevation – in this case, the value of each “pixel” is the measurable elevation of that point on the landscape. Neat, right?
Check out some of my posts about different types of raster data:
Remotely Sensed Imagery – satellite imagery, aerial photographs, and so on
Digital Elevation Models – or DEMs, the raster files that deal with elevation