CaSIL Map Interface

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Imagery Acquisition Coordination

Frenquently Asked Questions

California Mapping Coordinating Committee

California GIS Council

CERES

USGS

FGDC

Environmental Information Catalog

CalSpace UCD

The California Spatial Information Library

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.

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 DRGs 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 DRG Image Labels layer helps you identify which DRG image you are looking at. This is in contrast to the DRG boundaries layer, which identifies the extent of DRGs, and enables you to download the appropriate DRG. The "DRG Image Labels" 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 DOQQs layer displays the actual DOQQs, which are visible at scales higher than 1:100K.

The CalView Boundaries layer provides unique identifiers associated with the extents of CalView (Landsat) imagery. For instance, all CalView imagery for the San Francisco Bay Area will have the Path/Row identifier 44034.

The CalView Landsat layer displays the CalView imagery (at the default resolution of 30 dpi). This layer is only visible at higher scales, and it is not activated by default when you launch the service.

The Hillshades layer, displayed when you start the map service provides a suitable California background for scales above 1:250K.

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

The HiRes DOQs are high resolution, color, 1 foot DOQ imagery for the Stockton, Sacramento, and Delta regions. The download service is not available at this time. The HiRes Boundaries layer identifies the DOQ, using a US National Grid designation, whereas the HIRes DOQs display the actual high resolution DOQs themselves.

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, the DOQQ boundaries layer, or the CalView boundaries layer is not activated. You will need to reactivate the appropriate layer for the imagery you wish to download, 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 HiRes DOQQs imagery actually located?

The best way to see the extents of the HiRes DOQQs is to disable all layers except for the "Counties" and "HiRes Boundaries" layers. The HiRes Boundaries layer appears in a link pink color. For performance reasons, please note that the HiRes DOQs will only be visible at scales larger than 1:50000. Also for scales between 1:9000 and 1:50000 scale, you can toggle between the HiRes 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 HiRes DOQQs are visible between 1:9000 and 1:50000 scale. The CalView imagery are visible between 1:295000 and 1:4500000 scale.

Last Updated: September 7, 2004