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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.

Your recallNot started
Process

Distinguish between point, line and area sampling.

Process

Describe systematic sampling.

Process

Give three ways to reduce measurement error in fieldwork.

Questions from this subtopic

Each one with the model answer underneath.

  1. 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. 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. 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. 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. 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. 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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Sort every topic into what you know and what you do not, then drill only the weak ones.

Hotter magma is .
runnierthickerslower

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Rapid timed gap-fills on the terms and numbers you need to recall without thinking.

AThe lower quartile is the 2nd value, 11 cm.
BThe upper quartile is the 6th value, 16 cm.
CThe interquartile range is 16 − 11 = 5 cm.

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Assemble a full-mark answer from its marking points, in the order an examiner wants them.

The sunspot cycle lasts about 11 years.
TrueFalse

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Spot the fault in a statement. The traps are the mistakes students actually make.

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Short focus games to reset attention, so the next set lands better than the last.

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Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.

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