Index Datasets

An index dataset is simply a pointer to a selected file type which resides in a selected folder or folders.

In itself the index dataset does not contain any data; instead it tiles together other dataset files in a rectangular grid making a continuous map base.

For instance if you had 20 OS(GB) Meridian tiles in C:\DATA\OS(GB) Meridian_SS\SS68.ntf and another 12 in C:\DATA\OS(GB) Meridian_TL\TL02.ntf , you can create an index dataset pointing to these tiles in both folders.

Each time you load the index dataset in Overlays all the OS(GB) Meridian tiles in both folders are automatically loaded together on screen.

Advantages of using Index Datasets

  1. When new files are copied to indexed directories, they are automatically loaded to the indexed dataset.
  2. Your computer's memory may struggle to handle large volumes of map data. But with an Index, the computer opens map tiles as you pan to them and closes them as you pan away. This gives you seamless mapping when moving around the screen.
  3. An Index allows you to limit the number of files open on screen. This is useful when your computer has limited RAM and performance slows when a lot of tiles are open at once. By setting the limit on open tiles option to a lower number (the default is 64), you can avoid performance issues.
  4. You may use multiple paths and/or file types. This enables you to access files which are in several different locations (e.g. some on your computer’s hard drive and some on the network server) or files of different types (e.g. some raster files in BMP format and the rest in TIFF).