Map Overlays for Google Earth

Map overlays provide a way to substitute a map image for the default aerial image in Google Earth. I’ve previously provided a link for Google Maps and other map overlays for Google Earth. These maps are usually an improvement over the aerial imagery, but they aren’t always that clear, and often the roads are labelled incorrectly, especially in the Forests.

Detailed Stanislaus Forest Quad Maps

I usually use the quad maps from the environmental review of the Motorized Travel Management Plan to plan rides in the Stanislaus because they are very detailed. They include minor trails, and they are reasonably up to date. I’ve started making a (fairly) seamless Google Earth overlay of the maps including the index sheet, and I’m making the overlay available for download as a .kmz file. Just download and open the file with Google Earth to make the quads available as overlays.

USFS Stanislaus Quad Maps

USFS Stanislaus Quad Maps as a Google Earth map overlay

Stanislaus Quad Maps Index. Cherry Lake North Quad is selected.

Stanislaus Quad Maps Index. Cherry Lake North Quad is selected.

I set these up using the crudest of approaches–they don’t auto-load as you pan around. Given the limited region they apply to, this is fairly acceptable. Selecting all the quads at once will slow things down considerably, so use the index to choose the quads you need. The quality of the overlay images is not as good as the pdf files available on the Stanislaus Forest web site, but the overlay will get you oriented and let you know which pdf file to look at if you need more detail.

The transparency slider can be applied to any layer in the map.

The transparency slider can be applied to any layer in the map.

Use the transparency slider at the bottom of the Places panel to adjust the transparency of the maps or index.

For more information on these maps please see the Stanislaus Forest page. I’ll finish converting the rest of the quads eventually and will post an update.

High Quality Map Overlays from CalTopo

CalTopo is a web mapping application created by Matt Jacobs to support his work with Search and Rescue operations. CalTopo can display gpx and kml files, but it doesn’t support all kml features. I’ve been able to display simple tracks, but it doesn’t work with the Tuolumne Bikes map. Where CalTopo really shines is in displaying and blending map layers, and the map layers available on CalTopo are remarkably clear. Fortunately, he has made the maps available as Google Earth overlays with image tiles or as network links.

The maps that caught my eye were very clear USFS topographic maps, USFS Visitor Maps, USGS topographic maps, and two age ranges of historic USGS topographic maps.

Caltopo Overlays

CalTopo Overlays for Lyons Reservoir

To try the overlays visit and click the KML link opposite “Layers” in the panel on the left. There are two options: custom downloads and Superoverlays.

The Superoverlays at the bottom have network links and cover the 50 states–the map tiles are loaded as needed when panning or zooming in Google Earth. I have found that they work fine as long as a single Superoverlay is opened in Google Earth first and is allowed to load before opening another kml file (such as a Tuolumne Bikes map). The Superoverlays do not appear to work if moved to “My Places”; they have to be loaded each time by opening the file. Mr. Jacobs is not Google, and it’s safe to assume he can’t afford to run a wide open map service with unlimited access for the entire US.

To make a custom overlay on CalTopo, choose a map type at the upper right corner of the screen, choose a zoom level and the extent on the map, and click to download a kml file with network links or a kmz file with image tiles. If you intend to use the overlay more than once, the kmz will reduce demands on CalTopo and will be the most dependable, but the download will be large and the map won’t be updated if changes are made to the source. Please read the CalTopo “about” page, and if you become a user, consider making a donation.


QUADS is a free web application for “visualizing USGS quadrangle boundaries in Google Earth that provides an easy-to-use framework for retrieving georeferenced PDF topo maps from the USGS Store.” There’s good documentation for QUADS on the website of Metzger + Willard, Inc, it’s creator. I’ve found QUADS to be useful in two ways.

First, QUADS provides seamless USGS topographic map coverage, and it’s not restricted by the limitations for the CalTopo Superoverlays. Just download the file, open it and select “Layers” in the “Overlays” folder. Save it to “My Places” and turn it on when you need it. It’s a little bit slow, but dependable. The maps are good, but not as clear as the CalTopo maps.

QUADS USGS map, Lyons Reservoir

QUADS USGS map for Lyons Reservoir

The second way QUADS is useful is for its intended use. When I’ve tried to use the USGS Store, I’ve usually had browser problems. QUADS works and really is much simpler because Google Earth has an interface that is more suited to the task than the interface on the USGS Store site. Download the White Paper on the QUADS website for a good explanation of how to use the “Search Results” folder in QUADS to find and download various versions of USGS maps from the USGS Store.

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