The power of GIS lies in analysing multiple data sources together. Often the answer you are seeking lies in many different layers and you need to do some analysis to extract and compile this information. One such type of analysis is Points-in-Polygon. When you have a polygon layer and a point layer - and want to know how many or which of the points fall within the bounds of each polygon, you can use this method of analysis.
Given the locations of all known significant earthquakes, we will try to find out which country has had the highest number of earthquakes.
For convenience, you may directly download a copy of the dataset from the link below:
You may see some error messages as QGIS tries to import the file. These are valid errors and some rows from the file will not be imported. You can ignore the errors for the purpose of this tutorial.
ne_10m_admin_0_countries.zipfile and click Open. Select the
ne_10m_admin_0_countries.shpas the layer in the Select layers to add... dialog.
earthquake_per_coutry.shpand Click OK.
Be patient after clicking OK, QGIS may take upto 10 minutes to calculate the results.
PNTCNT. This is the count of number of points from the earthquakes layer that fall within each polygon.
PNTCNTfield and the country with highest count will be our answer. Click 2-times on the
PNTCNTcolumn to get it sorted in descending order. Click on the first row to select it and close the Attribute Table.
We determined from the simple analysis of 2 datasets that China has had the highest number of major earthquakes. You may refine this analysis further by taking into consideration the population as well as the size of the country and determine which is the most adversely affected country by major earthquakes.