Travel Advice - How to use the map index and the grid reference to find locations

Good quality maps contain an index that lists the names of places located on the map, as well as a notation describing their position on the map.

• It is a little known fact that many cartographic publishers may have more places named on the map than they have room for in the index and, often, delete names from the index in the interest of space.
  • If a place that you want to visit is not in the index, look on the map in the general location (if you know it) and you may find it sitting there in all its glory.

Street or place names listed in the index are associated with a grid reference number that identifies these locations on the map. The grid reference number points to a grid cell on the map or in the case of a road atlas to a page and then a grid cell on that page.

The number of grid cells varies based on the size and scale of the map, as well as the density of the information symbolized on the map (see What does scale mean and how to use it?).

• Large sized cells make it easy for the cartographer to create the index but make it very hard for users to find locations, since each grid cell may contain a large number of town or street names.
• Conversely, small sized grids make it easy to find places, since there are usually few names in each cell, but the grids may be hard to work with due to the great number of cells symbolized.
  • In addition, when the grid cells are numerous the cell notation scheme can become quite complex.

Normally, grid reference is given in the form of a pair of coordinates (e.g. 1, 5, or B, 2). Cartographic convention dictates that the first grid reference should be found along the bottom or top of the map and the second along the side of the map.

• Most map publishers have converted to a form of indexing known in the mapping industry as “Bingo Referencing”.
• "BINGOing" makes finding the location on the map just like playing Bingo.
  • You find the column and, then, the row identifying the cell and "Bingo" your town will be somewhere within that cell (this is the reason that most maps are indexed with a combination of alphabetic and numeric coordinates).

One trick of the cartographer’s trade is to show towns too small to be portrayed at the scale of the main map on "inset maps" (small maps set off from the main map and usually placed around the edges of the map sheet).

• Inset maps are shown in a larger scale to present greater detail than is possible on the main map.
• Another one of the relatively unknown rules of map making is that cartographers index the streets and towns shown on their maps at the most detailed scale possible.
  •  Even if a town is shown on both the main map and in an inset, the town will frequently be indexed to refer to the inset rather than the main map, since the inset is a more detailed representation.

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