1. How do I navigate with this interface?

You can zoom in and out using the magnifying glass buttons . You can click on a point on the map to zoom in or out. In the case of zooming in, you can draw a bounding box of the desired zoom extent, by first clicking and holding on the start point with your mouse, then dragging to the desired extents of the box, and releasing the mouse button.

You can pan the image by first selecting the pan tool . You can then click on the desired center point of the image. You can also pan the image by first clicking and holding on one part of the image, then drag to a different part of the image.

You can zoom to the initial extents by clicking on the button that looks like California ,
and move back and forward in your zoom history with the zoom history buttons .

A reference map at the lower left portion of the browser window allows you to quickly move to other areas of the state, by just clicking on a point on that image:

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2. What are the layers I can select?

The "DRG Boundaries" layer displays a standard USGS quadrangle grid that you can use to download DRGs. The layer is activated by default when you launch the service. The identifier and name of each quadrangle grid is labeled behind a yellow background (the labels look like Yellow Post-IT notes).

There are three DRG boundaries layer, each corresponding to the C (1:250K), F (1:100K), and O (1:24K) series. Initially, you will see the C DRG boundaries layer; as you zoom in closer, you will eventually reach the F layer, and finally the O layer.

When you zoom to a scale of 1:250K, you will be able to browse the DRGs. The "DRG" layer is activated by default. Like the DRG boundaries, you will first see the set of C series DRGs, followed
by the F series DRGs, and finally the O series DRGs.

The "Image Labels" layer helps you identify which DRG you are looking at. This layer is described below.

For the DOQQs, the "DOQQ Boundaries" layer displays a grid of standard USGS quarter quadrangles (quarter quads), that you can use to download DOQQs. Note that the layer is not activated by default when you launch the service. The identifier of each quarter quad is labeled behind a white background (the labels look like white Post-IT notes).

The "Hillshades" layer, displayed when you start the map service, are Digital Elevation Maps that provides the background for scales above 1:250K. Two such layers are provided, each sampled at a different resolution: one at 30 meters per pixel, and one at 90 meters per pixel.

There are also the County boundaries layer and Major Roads layer, along with corresponding labels.

3. How do I determine which DRG/DOQQ image I am looking at?

For DRG images, with the "Image Labels" layer, the identifier and name of each DRG is labeled behind a white background (the labels look like White Post-IT notes).

This "Image Labels" layer is not activated by default; you will need to enable it when you see the DRGs, and if necessary, turn off the DRG boundaries layer to avoid clashes between the white labels (DRG images) and the yellow labels (DRG boundaries).

For DOQQ images, with the "DOQQ Boundaries" layer, the identifier of each DOQQ is labeled behind a white background (the labels look like White Post-IT notes).

4. How do I download DRG/DOQQ images?

You first need to select the images you want to download. You do this by first selecting the query tool . In the pull down box, select either "DRG Boundaries" to query and download DRG images, or select "DOQQ Boundaries" to query and download DOQQ images. Once this is done, then either click on the quad/quarter quads you want to download, or draw a bounding box containing all the images you want to download.

The results will show up at the bottom of the browser window. Clicking on the links take you to a page, where you can download from our various mirrors.

Note: As a general rule, when downloading Tiff images, please right click on the link, and choose "Save Target As" for Internet Explorer users, or "Save Link Target As" for Mozilla/Netscape 7 users.

5. When I try to query for images, I get back zero results. Why is that?

Either the "DRG boundaries" layer, or the "DOQQ boundaries" layer is not activated. You will need to reactivate the appropriate layer, and perform the query again.

6. When are the DOQQ images visible?

The DOQQ images are visible at 1:100000 scale and higher.

7. Where are the (Stockton) Delta DOQQs imagery actually located?

The Delta DOQQs are for the Stockton delta area. You can access it directly by clicking the following link (note how the bounding box for the region is passed along with the URL):

Stockton Delta DOQQs

You will need to zoom in, at scales higher than 1:100000 to actually see the Delta DOQQs. Also for scales between 1:9000 and 1:100000 scale, you can toggle between the Delta DOQQs and the regular DOQQs.

7. Why do I get a blank, white screen?

There are two likely reasons:

• None of the layers are activated; make sure you activate at least one layer.

• If you did select a layer, check to see if you have zoomed in too far. The DRGs are visible between 1:24000 scale and 1:50000 scale for the C, F, and O series. Currently, the DOQQs are visible between 1:9000 and 1:100000 scale, whereas the Delta DOQQs, since they are at a higher resolution, are visible between 1:3200 and 1:100000 scale.