Q1. The column being mapped originally is the C02 emmissions by country. The column corresponding to GDP is "GDP_USD"
Q2. To display GDP we will be using a sequential color ramp as the data is interval based. Here is the color scheme found on Color Brewer.
It is certainly possible to have made the internet access map as a dot-density map and the telephone subscription map as a proportional map. However, the data may have not been as clearly represented if we had done it this way. This is determined by the magnitude of values we are dealing with. The dot-density seems to be the better option when dealing with many samples like we see in the telephone set.