Why are raster pyramids built in GIS?

Raster pyramids are built primarily to improve the speed at which raster data is displayed on the screen. When large raster datasets are used, rendering every single pixel at full resolution can be computationally intensive and slow down the performance of the GIS application.

By creating raster pyramids, which consist of reduced-resolution versions of the original raster data, the software can quickly display these lower-resolution images when zoomed out, allowing for faster and more efficient viewing, particularly when working with large datasets. As users zoom in, the higher resolution images are used. This process optimizes display performance and provides a smoother user experience when navigating and analyzing large raster files.

The other options, while related to raster data, do not accurately describe the primary purpose of raster pyramids. Reducing file size is a misconception, as pyramids do not reduce the size of the original data but rather create additional files for display purposes. Enhancing color depth and layering are not directly relevant to the function of pyramids either.