Measuring changes in land use

This is a graphic of Houston, Texas, showing how it has grown over the last twenty years. This image was created by comparing the amount of vegetation in a satellite image from the 1970's with a similar image from the 1990's. Red areas have very little vegetation in either of the images, indicating that they are historically urban, such as the downtown district. Orange and darker green/orange are similarly historic urban areas, though not as densely built upon. Green areas indicate vegetation, and light green regions are historically residential and suburban. The light and dark purple colors, however, represent areas that were built up between the time of the 1970's image and the 1990's image. In the first image, these areas showed a large amount of vegetation. But by the 1990's image, these areas show large amounts of urbanization, with the dark purple neighborhoods having the most. As you can see, most of this urbanization has taken place near the outskirts of the city, due to its growth and expansion.

Credit: Museums Teaching Planet Earth

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