The U.S. Geological Survey (USGS) publishes three seamless statewide USGS Quad Map layers:
The Arizona MapGuide map features all three USGS Quad Map layers, the Main MapGuide Map has the 1:24,000 scale USGS Quad Map, and the Pictometry Aerial Photos application may display a 1:24,000 scale USGS Quad Map image when there is no Pictometry oblique photo in the area.
You may be familiar with the paper version of these U.S. Geological Survey (USGS) Quad Maps that can be purchased at many map outlets. They are popular with anyone who needs detailed maps that include elevation contours and are often simply called "topo maps". The most common Quad Maps are at 1:24,000 (7.5 Minute) scale.
A digital raster graphic (DRG) is a scanned image of a U.S. Geological Survey standard series topographic map. The Arizona MapGuide map shows over 2,000 DRG Quad Maps as one big interactive map!
Quad Maps include a map "collar" which is a white border that include legend and other information. For this interactive map, the collar has been clipped off and the maps have been georeferenced to align with each other in a seamless grid. Due to variations in the individual Quad Maps, the seams are often visible on the Arizona map.
The USGS produces a whole series of topological maps. The USGS has a good description of the different USGS map series, including the three shown on the Arizona map: 1:24,000 (7.5 Minute), 1:100,000 and 1:250,000. In addition to being at different original paper map scales, each of the three Quad Map layers have other differences. The TopoZone is a good source for viewing USGS Quad Maps for the entire United States, along with more information on the maps, such as map symbols.
Generally, interactive maps such as MapGuide maps are designed to be viewed at any scale. More detail becomes available as you zoom in and identifying labels scale to match the current view. Most users are not aware of this because the map looks "right" regardless of scale.
Each USGS Quad Map series was designed for viewing at one scale -- the scale of the paper map. Other than using a magnifying glass, you can't pan and zoom a paper map. It's just one scale and that's it. With these paper maps scanned as DRGs and input into the MapGuide system, the MapGuide viewer allows panning and zooming at any scale, close up or far away. This has the effect of showing the maps at viewing scales they weren't designed for. Therefore, you can't see all the detail that was on the original paper map when you are zoomed way out. It's like looking at the paper maps from a distance of 50 feet or so. Conversely, if you zoom way in, you will see a blowup of a very small area as if you were using a magnifying glass on the paper map. For this reason, the Arizona MapGuide map includes Quad Maps of three different original paper scales. You can choose the most appropriate of the three original Quad Map scales for your current zoom level as separate layers in the legend to the left of the map area.
To keep your map viewing as fast as possible, have only one USGS Quad Map layer on at the same time. If more than one Quad Map layer is turned on, it will cover the others that are still there and taking processing time when you pan and zoom. This includes the USGS DOQQ Imagery as well. It's not useful to have a USGS Quad Map layer and the USGS DOQQ Imagery turned on at the same time. Remember that the MapGuide legend layer order shows the order that displayed layers are "stacked" on the displayed map. Turning on a Quad Map layer or the USGS DOQQ Imagery covers all active layers below it.
The Quad Map layers on the Arizona map are referenced to the NAD 83 UTM projection, Zone 12. No Quad Map updates are planned for this MapGuide map.
There are three USGS Quad Index layers on the map, one for each Quad Map layer resolution - 1:24,000 (7.5 Minute), 1:100,000 and 1:250,000. The USGS Quad Index layers are grids showing the area covered by each of the original paper maps. Holding the mouse cursor over individual map areas shows yellow map tips with the Quad Map name, map revision date and map publication date where available.
In addition to the U.S. Geological Survey, we thank the BLM GIS Incident Management Team for clipping and georeferencing the USGS maps and photos, and the Arizona State Cartographer's Office for duplicating the stacks of CDs to make them available to us. This Arizona MapGuide map would not have been possible without their efforts.