The ASCII Grid file format (.asc) is a plain text file format used to represent raster data, typically elevation models, climate data, or other spatial data. It's a simple and widely supported format, making it useful for exchanging data between different GIS (Geographic Information System) and spatial analysis software packages. The file consists of a header section containing metadata about the grid, such as the number of rows and columns, the cell size, and the coordinates of the lower-left corner. Following the header, the file contains the actual grid data, with each line representing a row of the grid and each value representing the data value for a specific cell. Missing or invalid data values are often represented by a specific 'NODATA_value' defined in the header. Because it's a text-based format, ASCII Grid files can be easily inspected and edited using a text editor, although this is generally not recommended for large datasets due to performance limitations. The simplicity of the format makes it a good choice for data archiving and interoperability.