The majority of Greenlandic homes are traditional gable-roofed timber structures. Most structures have lasted well due to the combined impacts of tradition, malleability, and a long-established supply route from Denmark. However, modern buildings are now appearing on the market. There are also a large number of tents used for living quarters during summer months when ice caps melt and rivers flow free. These tent cities often contain several thousand people who come together to build new lives as they try to find work in the small fishing industry or go looking for better jobs in Europe or North America. Greenland has one of the highest rates of electricity usage per capita in the world. This is mainly because there's a lot of cold that needs heating at night, so most houses have roofs covered in asphalt tiles or metal sheets which heat up when sunlight hits them. The resulting hot air is drawn into houses through open doors and windows. Each year, nearly all Greenlanders travel by plane to reach distant parts of the country for work or school. The need for transport means that people live near where they work or go to school, so there are many small towns with streets full of similar houses.