What are the signs by which you can group the countries of Eurasia

The countries of Europe can be grouped according to different criteria. The most common is grouping by population, by the size of GDP per capita. By the size of the state budget, by the duration of highways, or railways. Yes, whatever. For example, you can countries by the number of cities, by the number of people employed in agriculture, and so on. Thus, classifications and criteria for sorting can be found very much, depending on how to classify.