NR 322: Scale and Resolution

Jim Graham & Alex Daniels

Fall 2010

Chapter 2

http://jan.ucc.nau.edu/~rcb7/namNm15.jpg

Scale

• Scale is the scale of the map relative to the true size of the items on the map

• e.g 1:750,000– 1 unit on the map is equivalent to 750,000

units on the earth

• Small scale vs Large scale

• Which number is larger– 1 / 750,000 or 1 / 2

Map Scale

Misunderstood Terminology

• Small Scale = Large Extent– Think of the divisions on the scale being small– Miles are smaller at small scale

• Large Scale = Small Extent– Think of the divisions on the scale being big– Miles are larger at large scale

• Recommendation:– Use Large Extent or Small Extent– Use Low Resolution or High Resolution

Scale can vary on a map

• What is the scale in kilometers on a Geographic Projection map?

Scale can Vary

• What is the scale on a google earth map?

Resolution

• Resolution is the ability to resolve detail

• We mostly refer to Spatial Resolution– For Rasters/Grids/Digital Photos this means

the size of the pixels.– What distance on the ground does one pixel

represent?

30 Meters

30m vs. 1m Spatial Resolution

Washington D.C. ~ 30m

Washington D.C. ~ 5 m

Resolution

• High resolution is awesome, why don't we make everything 1m data or better?

• The number of pixels increases exponentially as you increase spatial res.

Resolution x 2

Pixels x 4

High Resolution ~ Big Files

• Rasters and photos can get really big really fast.

• Civilian satellites now can take satellite photos as high as 41 cm resolution

• i³ in Fort Collins has 1m Satellite Photos that take 300 Gigabytes for just one area.

Low spatial resolution

• Low resolution averages data

Accuracy and Precision

• Accuracy is how close something is to the true value

• Precision is how close of a measurement you can make

• High accuracy doesn't mean high precision