Spatial Data Review

Refresher:

  • Points
  • Lines
  • Polygons

How do we deal with these things in a computer?

Data Model

  • a set of constructs for describing and representing selected aspects of the real world in a computer.
  • We need a model because the real world is infinitely complex.

raster vs vector

Raster files:

ncols 480
nrows 450
xllcorner 378923
yllcorner 4072345
cellsize 30
nodata_value -32768

43 2 45 7 3 56 2 5 23 65 34 6 32 54 57 34 2 2 54 6 ...
35 45 65 34 2 6 78 4 2 6 89 3 2 7 45 23 5 8 4 1 62 ...
43 2 45 7 3 56 2 5 23 65 34 6 32 54 57 34 2 2 54 6 ...
35 45 65 34 2 6 78 4 2 6 89 3 2 7 45 23 5 8 4 1 62 ...
43 2 45 7 3 56 2 5 23 65 34 6 32 54 57 34 2 2 54 6 ...
35 45 65 34 2 6 78 4 2 6 89 3 2 7 45 23 5 8 4 1 62 ...

Vector Data Model

  • More commonly associated with discrete data Concepts
  • Three general geometric types
    • Point
    • Polyline
    • Polygon

How do these look in the computer? It depends…

At the most basic level:

points lines polygons

What about shapefiles?

shapefiles shapefiles geometry

This is a lot of information and not particularly efficient.

That leads us to web mapping. Are shapefiles the way to go? Well, to understand why they aren’t, it’s helpful to understand a little about the internet.

  • Packet switching
    • Data are broken into small chunks and passed from an origin to a destination
    • Allows for many routes to the destination computer
  • Servers
    • Electronic filing cabinets that pass information when requested
  • Clients
    • Computers that get information from servers

the web