KML Custom Maps

By Robert Bennett,

This document describes the free KML custom maps available at and how to use them in your GPS device. Custom maps are saved in the KML file format and compressed (zipped) into the KMZ file format which contain one KML file and multiple map tiles that are used by many different hand held GPS receivers, for example the newer Garmin® devices. In addition, there is online and offline software, for example Google Maps® and Google Earth® that can display the map tiles packaged in KMZ files.

The following image is an example of a KML custom map loaded into Google Maps. KML-KMZ Custom Map

You can download this KML file (~274 kB) and display it in Google My Maps, Google Earth and Garmin GPS devices including the eTrex®, Colorado and Montana series. There are hundreds of custom maps available to download, free of charge, from this website.

There are many differences between the points that we plot on Google Maps and the points that we plot on custom maps. Let's take a look at some of these differences; the image in Exhibit L is visible on but the points in the image are not available to download. The points in the image are not available to download because a computer algorithm simplified the points before they were plot on the image. The points were simplified because the image is just a summary of the trail. This is why the red lines that connect the points are straight lines.

Exhibit M is an example of a custom map that you can download to your GPS device. Compare the points in the exhibits where the arrows are pointing. The points on the custom map were not simplified as in Exhibit L. In addition, the points are plot over a USGS 7.5 minute topographic base map with mile-markers and waypoints. As you move along the trail, you can use your position and heading on the custom map as a position reference for your paper map.

Exhibit L, M, N

EXHIBIT L: This is a section of the Tahoe Rim Trail plot over an aerial photograph in Google Maps that is visible on the web site. Notice the points connecting the lines were simplified with a computer algorithm. While the points were simplified, they remain very accurate.

EXHIBIT M: This is a custom map for GPS devices. It's the same trail represented in Exhibit L, except the points are not simplified and the scale is larger. The red and white arrows are pointing at the same location. Notice the differences in the points on this map compared to Exhibit L.

EXHIBIT N: This is the same custom map represented in Exhibit M, except the scale is reduced. Notice each point representing the trail is occupying approximately 40 square feet. The numbers on the trail are mile-markers. Some custom maps include additional waypoints.

The following exhibits are photographs of a hand held GPS receiver displaying a custom map. In Exhibit P, the map scale is 800 feet and we can see the start marker (large solid circle) the trail (solid, dark curved line) and current position (solid triangle) which also indicates the current heading. When the GPS receiver is moved (for example when a person hikes with the GPS receiver) the current position and heading is updated.

Exhibit O, P, Q

Download Custom Maps

The procedure for downloading custom maps to a hand held GPS receiver depend on the manufacturer and model of the device used. When some GPS devices are connected to a personal computer with a USB cable, the GPS device is recognized as an external hard drive. In this instance, downloading a custom map to your GPS device is as easy as clicking the download link on web pages and then selecting a specific folder (defined by the GPS manufacturer) in the device. Click OK to download. After the GPS device is disconnected from the USB cable, the custom map is selected from a menu in the GPS device. Please read the GPS device instructions for additional information.

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