Simple Random Sampling ✓

Selecting a sample by simple random sampling requires you to specify the study area and a sample size.

  1. Start by running the Sampling Design script in the Scripts pane.
  2. In the first entry box Specify an image ID and sampling scheme, specify a map that defines the study area. Because you are not using strata or clusters, the contents of the map does not matter.
  3. Under Specify band if a multi-band map (if not, specify 1): if you are using a map that contains multiple bands, specify which band you want to use to define the study area. Otherwise, just specify “1”.
  4. If the map has a no-data value or if you want to exclude a certain value in the map when defining the study area, specify the value in Specify no data value.
  5. Click Load image – the map should be displayed in the image pane.
  6. Under Select a sampling scheme, select Simple Random
  7. Under Determine sample size, you can either specify an arbitrary sample size or determine the sample size by specifying a target standard error of the anticipated overall accuracy of the map that is being assessed.
If specifying arbitrary sample size
  1. If choosing to specify an arbitrary sample size, simply add a number under Specify sample size.
  2. Click Create sample.
If specifying a target precision
  1. To determine the sample size required to meet a certain target standard error of the overall accuracy, first specify the anticipated overall accuracy of the map you are assessing under Specify anticipated overall accuracy (0-1)
  2. Then Specify target standard error of overall accuracy (0-1) and click Calculate sample size – the sample size is calculated using Equation 12 in [1] which is derived from Equation 4.2 in [2].
  3. Click Create sample.
  1. To view, the sample in the Display pane, click Add to map
  2. To export the sample, click Export sample and select the desired file format.
[1]Olofsson, P., Foody, G. M., Herold, M., Stehman, S. V., Woodcock, C. E., & Wulder, M. A. (2014). Good practices for estimating area and assessing accuracy of land change. Remote Sensing of Environment, 148, 42-57.
[2]Cochran, W. G. (1977). Sampling techniques. John Wiley & Sons.