Figure4
![Tools for planning large-scale measurement surveys for the assessment of indoor environmental pollutants: the case of radon](https://image.oaes.cc/d728a6a1-e14f-45d7-9907-986826e0526e/jeea3034-4.jpg)
Figure 4. Grid square (1 sqkm) in which SPT indicates a sample of 3 dwellings to be selected for making indoor radon measurement. The background map shows building polygons and addresses. From the attribute tables of the open-source vector data, residential buildings can be distinguished. SPT: Sampling Plan Tool.