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    Geographic Information Systems Lab

    Map tool usage


    As described throughout this document and in the training sessions, the EBI is a composite of three data layers: Water Quality Risk, Soils Risk and Habitat Quality. These data layers each contribute information at different spatial scales. The map tool allows a user to view how each of the layers independently contributes to the overall EBI. The tool is based on slider bars which adjust the transparency of the three different layers. It uses a Google-like open map platform that allows the user to pan and zoom around the map, turn on other layers of interest, and explore the EBI data. Guidelines for using this tool are presented below:

    General navigation

    You can drag the map around with the left mouse button, as long as you don't click on a CRP parcel at the same time.  Just avoid CRP parcels when dragging the map.  The mouse wheel can be used for zooming in and out.  The blue and white controls in the top left can also be used for panning and zooming.

    To zoom in on a particular area quickly, hold the Shift key, then draw a box around the area of interest with the mouse.

    Changing basemaps

    To change base maps (the road, sattelite, or topo. image in the background), click the blue and white plus symbol at top right.  A list appears, you can only select one basemap at a time.  Click the blue and white minus symbol at the top right of the list to get it out of the way.  The list can also be used to turn on and off the EBI, SPI, Erosion, and Wildlife overlays, but it's better to use the controls below the map for those, as described below.

    Examing EBI, SPI, Erosion, and Wildlife grids

    Below the map are four lines of overlay controls, one each for the EBI, Erosion, SPI, and Wildlife grids.  To turn on a grid, check its checkbox.  To change the opacity of a grid, move the slider next to it.  This allows you to see how the EBI grid is built up from the other three, and how each contributes its influence to the final EBI.

    Whenever you move the map, the grid overlays are turned off.  This is to keep the load on the server manageable as you move around the landscape.  Just check the layers of interest back on when you've repositioned the map to where you want it.

    (For the technically inclined, the overlays are rendered as tiles on demand and then placed in a Tile Map Service (TMS) system.  With all four layers turned on a single user can easily generate 50-100 near simultaneous rendering requests as they pan and zoom across the map).

    CRP parcels

    As well as changing the basemap, the list accessed through the blue and white + symbol at the top right can be used to access the the checkbox for turning the CRP parcel boundaries on and off.  These boundaries are only available when you've zoomed in on the map to the point where the scale at the bottom reads 2km / 2mi.  If you zoom out beyond that level you can't view the CRP parcels.

    The CRP parcels displayed are not necessarily up to date and should be used only for exploring the general relationship between CRP parcels and the EBI, any particular parcel may or may not be currently enrolled in the CRP program.

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