Satellite Images

Aerial imagery programs provide more detailed coverage of smaller areas. Figure 1.6 shows the difference in coverage extent between a Landsat satellite image and an image captured by an aircraft. An aircraft with a Microsoft Ultracam Eagle sensor captured the image on the right. In this image, Horseshoe Falls, the Canadian side of Niagara Falls, is clearly visible. It was captured from an altitude of about 5,850 m. The image on the left is a Sentinel-2 image and was captured from an orbit of 786 km. The Sentinel-2 image covers a much larger area and shows much less detail than the red rectangle on the Sentinel-2 image, indicating the coverage of the aerial image.

Remember the definition of scale from the reading in Section 1.2, "Scale is the ratio between the distance between two locations on a map and the corresponding distance on Earth's surface". The distance between two locations on the aerial image is larger than the same distance on the satellite image. Thus, the aerial image of Horseshoe Falls is considered a large-scale image, and the Sentinel-2 image of the same area is considered a small-scale image.

All of these technological components, including GIS, comprise what we call geospatial technology. The term geospatial may seem redundant, but remember that "geographic" refers to particular locations, and "spatial" refers to the position, size, and area of things. Thus, geospatial technology refers to technology that helps us capture and analyze places and the relationships between those places.

These varied applications of geospatial technology reflect the breadth of geography. The next section introduces some of its subdisciplines and specializations. You will see that GIS actually pervades many of these subdisciplines and specializations.