NRSC 2230 / GEOG 2750

Scale

Overview

One of the issues we must deal with when working with spatial data, is how to represent real-world distances and measurements in our system that contains limited space.  To solve this problem, geographers and other users of spatial data have presented scaled portions of the Earth’s surface.

Learning Objectives

Upon successful completion of this topic you will be able to:

  • Explain what is scale (factor)
  • Explain the differences between large scales and small scales
  • Explain the difference between the terms “accuracy” and “precision”

What is Scale Factor

Scale Factor (commonly referred to simply as scale) is the amount of reduction used to convert the spatial features from real-world units into page units.  This value is expressed as a ratio (e.g. page unit : ground unit).

e.g. 1:10,000 => a reduction in size / detail by 10,000 times
conversion to scale statement  => 1cm = 10,000cm (or 1cm = 100m)

A larger scale is thus reduced by a lesser amount. Hence 1:50,000 is a larger scale than 1:250,000. One unit on the map represents a smaller area so more data can be presented.

Source:http://gis.unbc.ca/courses/geog300/lectures/lect2/index.php

Activity 1 – Getting Further Information

a) Use the links provided below to get further information on scale and the use of scale in representing spatial data.

Note: These open in a new window

Natural Resources Canada – Scale

Natural Resources Canada – Map usage

 

Please feel free to search further using any internet search engine.

b) View the short video giving a brief explanation of calculating distance using the map scale

Video:

Calculating Distance

Activity 2 – Making Decisions on Scale

Based on the information gained from your internet searches, please provide an entry in your blog as follows:

An entry that discusses the type of maps used in your area of study that can be presented at a small scale and the type of maps that must be presented at a large scale.  Please provide your reasons.

Note:

You may discuss this with a partner.  If you work with a partner, each student is to provide an individual blog entry and must indicate the name of the partner.

Activity 3 – Your Comment on Scale

Please provide a comment on at least one of the discussions presented by another member of the class (not your partner)

Accuracy vs Precision

The terms Accuracy and Precision are often used interchangeably but have very different meanings.  The former is a reflection of how closely the location reflects the feature’s true position.  Precision is a reflection of how repeatable the measurement location is.

Activity 4 – More information on Accuracy / Precision

Please post a few paragraphs on Accuracy, Precision and the Types of Errors associated with GIS data ( use your favourite search engine).  Name the post  Accuracy and Precision in GIS.

Activity 5 – Please Help (optional)

a) If you found useful information at a site other than the three listed in Activity 1, please indicate the site or link to it in your Blog entry.

b) Please help in finding a internet video related to scale, that may be more suited to a Canadian audience e.g Canadian map etc.  Please post any suggestions to your blog by creating a link to it.