OCR A-Level Geography H481
Coastal Landscapes
Glaciated Landscapes
Dryland Landscapes
Earth’s Life Support Systems
Changing Spaces; Making Places
Trade in the Contemporary World
Global Migration
Human Rights
Power and Borders
Climate Change
Disease Dilemmas
Exploring Oceans
Future of Food
Hazardous Earth
Geographical Skills
Geographical Skills
Collecting data: sampling, measurement error and digital devices
- 3 things to know
- Components 01, 02 and 03
Overview
Recall questions on why geographers sample, random, systematic and stratified sampling, point, line and area sampling, sample size and pilot studies, systematic and random error, accuracy and precision, the Powers roundness scale, reducing measurement error, collecting data with smartphones and their limits, and the benefits and pitfalls of geographical information systems.
What you need to know
Answer each one before you reveal it.
Describe systematic sampling.
Give three ways to reduce measurement error in fieldwork.
Questions from this subtopic
Each one with the model answer underneath.
- 1
Why do geographers take a sample rather than measure everything?
Model answer
A whole population, such as every pebble on a beach or every household in a town, is too large to measure, so a sample is taken that can be collected in the time available but still represents the whole.
- 2
Describe random sampling.
Model answer
Every member of the population has an equal chance of being chosen, for example by using random numbers to generate grid coordinates for the sample points within a study area.
- 3
Give one advantage and one disadvantage of random sampling.
Model answer
It removes the investigator's bias in choosing sites, but by chance it can leave parts of the area unsampled and may select points that are dangerous or inaccessible.
- 4
Describe systematic sampling.
Model answer
Samples are taken at regular intervals, such as one pebble measured every 5 m along a transect from the sea to the back of the beach.
- 5
Why is systematic sampling well suited to measuring change along a transect?
Model answer
Regular spacing gives even coverage of the gradient being studied, such as the change in vegetation inland across a salt marsh, although it can miss or exaggerate a pattern that repeats at the same interval.
- 6
Describe stratified sampling.
Model answer
The population is divided into sub-groups and each is sampled in proportion to its share of the whole, so if 60% of an alluvial fan is gravel and 40% is sand, 60% of the sample points are placed on the gravel.
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