CAP GRID INFORMATION
As you may have noticed, there are two major gridding systems used in Civil Air Patrol. Much of the information on this page relates to the "old" grid system, now called the Conventional grid system. The "new" grid system is now called the Cell grid system. Each system has advantages and disadvantages. Read below for generic information about CAP grids. You can find out specifics of the the Conventional and Cell grid systems by clicking the menu links to your left. Alaska has its own grid system, the specifics of which are also detailed on this website.
A grid is nothing more than a coordinate system of boxes. Latitude / longitude or UTM (Universal Transverse Mercator) coordinates are grid systems with which many people may be familiar.
Since we cannot search everywhere at once, CAP grid systems ultimately define a searchable area. This area can be readily communicated between people by use of the specified grid system. Both the Conventional and the Cell grid systems use latitude and longitude as a basis for establishing an area called a "quad." "Quad" is short for "quadrangle." This basically is just a rectangle shaped area bounded by lines of latitude and longitude. In fact, a grid is just a standard sized quad.
The basic areas that we use in CAP are the 15 minute quad and the 7.5 minute quad. The 15 minute quad extends 15 minutes of latitude and 15 minutes of longitude. The 7.5 quad is similar. You might notice that 7.5 is half of 15. This allows for four 7.5 minute quads to fit within one 15 minute quad. Typically in CAP we call these quads "grids." This is how the areas will be termed for the remainder of this discussion.
Each 15 minute grid is approximately 225 square (statute) miles of area. Because the difficulty of searching an area this large depends greatly upon the terrain and techniques involved, each 15 minute grid is often subdivided into four manageable sections, 7.5 minutes on each side. These sections are labeled, from left to right and top to bottom: A, B, C, D. Observe the table to the left for an illustration of this method. In addition to being essential in subdividing Conventional grids, this A-B-C-D arrangement is the key to understanding the Cell grid system.
Consider the following. Each is a 7.5 minute grid, or a quarter grid in the conventional system or a three-letter grid in the cell grid system. As an example, the Twin Cities sectional is at the northern extreme of the lower 48 United States sectionals at approximately 49º North Latitude. Quarter-grid MSP 23B is the same as grid 48095BAB, and measures 7.5 by 4.94 NM, which is at approximately 37 NM2. At the southern extreme of 32º North Latitude is the Brownsville sectional. The BRO 381D grid or cell grid 24097CCD measures 7.5 by 7.02 NM, which equals 52.7 NM2. All of the grids used in these examples are manageable search areas so long as consideration is given to the actual area being searched. Incidentally, a square nautical mile is equal to 1.323 square (statute) miles.
Coincidentally, a 7.5 minute quad is the exact same size as a 1:24,000 scale USGS map. While it is certainly not the only kind, this type of map is often referred to as a "topographic" map. The 7.5 minute quadrangle is generally the highest scale and shows the most detail for most areas of the country. As such, the 1:24k 7.5' quad is usually the best available for ground teams. If you wish to have this level of detail in mapping, you will need to do significant research ahead of an incident to determine what USGS 7.5' quadrangles cover your areas of interest. There are several mapping programs (such as the National Geographic "TOPO!" program) that include digital versions of these maps. Depending upon the size of your state, the storage space that may be required could be considerable. For example, digital raster graphics for all the USGS 1:24k 7.5' quads for the state of South Dakota require approximately 7 Gigabytes (7,000 megabytes) of storage space.
Regardless of which grid system is used, it is important that both air and ground crews are able to use the same map before (briefing), during, and after (debriefing) the mission. A popular map format is the DeLorme "Atlas & Gazeteer." These atlases include topographic maps of the entire state at a scale that is generally more useful than a Sectional Chart or a road map. While the detail will not be as good as a 1:24k topo map, it is often sufficient for aircrews and ground teams to have an excellent common frame of reference. A copy of this map book should be in every CAP airplane and vehicle. Because air to ground coordination is often not conducted under ideal conditions, a common map such as the DeLorme usually goes a long way in communicating necessary instructions. DeLorme also makes excellent software that can download GPS track files.
When flying to search a grid, preflight familiarization is essential. Ensure that you identify any charted hazards or obstacles within the grid. You should be able to find the boundaries of your grid using GPS, and without it! Pilotage is essential.. To back up these methods, use of VOR, DME, NDB, and Loran navaids should be practiced. Ground teams should practice locating grids on different map types and by driving to various locations.
To continue learning about CAP Grids, next go to the Conventional grid system page.
This page of the CAP Emergency Services Resources™ website was last updated 07/01/2008
©1998 - 2008 Scott E. Lanis. All Rights Reserved.