BaseCamp and contemporary Garmin devices allow the display of custom raster maps/images which reside in the \Garmin\CustomMaps folder located on the GPS (main memory or SD card). These maps are georeferenced and tiled KMZ files more often than not obtained by scanning a paper map to produce a JPG image, geolocating it using Google Earth, exporting it as a KMZ and then tiling it using software such as KMZFactory.

A user wishing to use aerial images as a backdrop for a GPS display can adopt much the same process as that employed to produce custom maps – the GPS is not able to recognise the difference between maps and aerial images as they are both raster scans.

Those particularly interested in using high-resolution satellite imagery and/or detailed proprietary raster maps as overlays might like to access the Garmin BirdsEye subscription service. This takes three forms – BirdsEye Satellite Imagery, BirdsEye TOPO and BirdsEye Select, each of which costs about £22 per year per GPS device:

• BirdsEye Satellite Imagery delivers an unlimited number of worldwide high definition satellite images.
• BirdsEye TOPO delivers high-quality 1:24,000 USGS and 1:50,000 NRC maps that offer a view of the terrain including points of interest such as car parks, camping areas, trails and water sources. The coverage area is the entire U.S and Canada, south of 68 degrees latitude. There are no download limits.
• BirdsEye Select delivers data directly derived from the most popular European paper maps and covers Germany, France, Great Britain and the Republic of Ireland, as well as the Kompass branded maps for Austria, the Eastern Alps (Southern Germany/Northern Italy) and Switzerland. The maximum area that can be downloaded as part of a single subscription is 600km². A UK map is based on the Ordnance Survey 1:25,000 series is available separately and provides 3,000km² of coverage for a single subscription.

When a subscription runs out, the images and maps already on the GPS remain usable but no further uploads from Basecamp are permitted until the subscription is renewed. Note that the maps and images are locked to a particular GPS device and cannot be transferred from one to another.

To say that this is a confusing array of products would be an understatement!

BaseCamp processes the licensing data and therefore must be used to both receive the images/maps and upload them to the GPS. Users recommend that the BirdsEye images be stored on an SD card and NOT in the main memory – failing to take this advice can result in non-recoverable device lockups.

BirdsEye allows up to 50,000 tiles at 5 zoom levels. In contrast, the number of custom map tiles that can be loaded at any one time is small – for the GPSMap 64 Series the limit is 500. Details may be found here.

The file extension for BirdsEye images is JNX. They reside in the Garmin\BirdsEye folder that can be found both in main memory and on the SD card. Unsurprisingly, JNX is a so-called tile format, ie large raster maps are divided into smaller rectangular pieces (tiles) to speed up the map rendering.

BirdsEye is supported by most of the more recent Garmin devices including:

Alpha 100, Astro 320/430/900, Colorado 300/400c/400i/400t, Dakota 10/20, Edge 520Plus/530/800, Edge Explore/Touring, Edge 1000/1030/1030Plus, Epix, Etrex 20/22/30/32, GPSMAP 62/64/66/78/86, Montana 600/650, Oregon 200/300/400/450/550, Overlander, Rino 610/650/655, and Zumo XT.

Full details are available here.

Use of non-Garmin JNX files

JNX files use a proprietary format which is not in general use. That said, the custom maps produced by QMapShack and its associated package QMapTool are generated in JNX format as standard – the need to employ Google Earth for georeferencing, then tiling using independent software is thereby avoided. In the absence of a BirdsEye subscription, a non-Garmin sourced JNX file placed on a Garmin GPS will not load and render unless a firmware patch is installed which modifies the licensing controls. This may be accessed via OpenStreetMap or downloaded directly from the patcher site. It works by removing the limitation on the number of demo-maps displayed and their maximum area. Use at your own risk!