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25 March 2009  

page update: 26 May 11


The MERLIN Electronic Atlas

Go to Merlin Online Atlas

These illustrations provide a summary of the information you can retrieve from the electronic atlas of Maryland's Back (Coastal) Bays. They also provide guidance in the key steps you need to navigate around in the atlas to locate and view all of this geodata. 

Home Level You return to this first screen
when you click on the Home Icon.

MainMenu2Four separate paths
There are four directions for exploration when you reach the main menu. A click on the Back Bays button takes you to a SPOT satellite image of the back bays and 27 overlay themes and their associated database information. The Statewide Watershed Information button brings up a Landsat satellite image of the entire state with a watershed boundaries layer and associated database information. The Back Bays branch of the atlas has the greatest depth and the most variety, so we'll use it as the example of how to use this atlas. Click on the box labeled Back Bays. A great deal of geodata is being prepared for viewing at this step. Please be patient; this may take time on a slow CD.

ToolBarUsing toolbar features
The toolbar in the atlas viewing window includes many useful functions. The entire image for the initial Back Bays screen is sized to fit your view window. This SPOT image is actually about 5000 lines by 4000 columns. The other geodata in the atlas are also large, so the ability to zoom in and out and reposition the view is necessary to get a detailed display of your area of interest. Move the mouse along the toolbar, pausing over each icon to review the ToolTip that identifies the button's function.

For example

1. Click the Zoom Box icon Zoom Box
2. Position the cursor at the upper left of the detailed area of your interest in the view
3. Click and hold the left mouse button as you drag the mouse down and to the right until the box created is as wide as desired.

4. Click the right mouse button to zoom in on thearea of the box (on a Mac, hold the Command key and click the mouse)

Area of box zoomed in
Zoomed In

The Back Bays hierarchy
The Back Bays portion of the atlas has three basic levels. At the first level, you view the SPOT image as a reference layer and turn on or off any of the overlay themes. The second level is the same geographic area but uses 11 adjacent 7.5' USGS topographic map quadrangles as reference layers and allows overlay of all the themes. The third level uses 36 adjacent 3.75' color-infrared orthophoto quadrangle maps as reference layers, and again you can overlay all the themes. (Only the SPOT image, Berlin 7.5', Berlin NE 3.75', and Ocean City NW 3.75' maps are at full resolution. The remainder of the maps are sampled.) You can move to the next reference level at any time by clicking the mouse at the point of interest in the current reference layer. The position of your mouse click determines which area of the next reference level is displayed. If you happen to click in a position where the individual quads overlap in the next level, the HyperIndex Link Selection window opens, and you can point and click to choose which of the overlapping quads to display.

Previous Level You return to a previous reference level
by clicking on the Previous Level icon.


HyperIndex Note: if you have been viewing database tables, making measurements, or using the Zoom Box or Slide View tool, you must switch back to the HyperIndex tool before you can use the mouse to move through the atlas.

How to see more
The SPOT image and quad maps provide a reference framework for the many themes, which are initially hidden. A Layer Controls window opens with each Back Bays reference layer and lists all the information themes available for viewing. When you choose to show a hidden layer, it is drawn on top of the existing image. Because geodata making up this atlas is read from CD-ROM, every layer drawn adds to display time.


Click on a layer
to select it.

The (-) mark means
the layer is hidden.

Click the Show Layer button
to turn the selected layer on/off.
LayerCtrlRdGrd 1. Scroll to the bottom of the Layer Controls list.
2. Click on the 7.5' USGS quad grid outlines in the Layer Controls window (for example, WORCGRID / QUAD_GRIDS) then on the Show Layer toggle button
3. Click on the State Highway Administration's Highway Mapping Team's roads layer (for example, ROADS / ROADS_YELLOW) then on the Show Layer toggle button


USGS 7.5' map quad outlines
State Highway Administration Roads


Redraw Clicking on the Redraw icon recomposes the viewing window, drawing all layers chosen for viewing in correct drawing order. You need to use this icon if you want to eliminate layers that were selected for drawing then hidden again. Also, polygons with solid fill colors in overlay themes become lightly tinted and transparent to the layers below when redrawn.
Choosing Locator from the View menu opens a small version of the full image that contains an elastic box to show your current view. This box can be repositioned and resized, and the effects are seen in the larger view window when you click on the Apply button.

Getting more detail

Only the Berlin NE color-infrared orthophoto quarter quad has an overlay theme with parcel maps and land ownership information. You can navigate to this level with a few well-positioned mouse clicks.

HyperIndex Click on the HyperIndex icon in the toolbar
with your view positioned as shown in the How to see more section, place the cursor over the creek below the cluster of roads near the upper right of the central map grid outline (the northeast quarter of the Berlin quadrangle), and click the left mouse button.
after the Berlin quad is displayed, click the left mouse button in the center of the view to move to the next level
scroll to the bottom of the Layer Controls window after the color- infrared orthophoto is displayed, click on the layer containing land parcel boundaries for this area (WORCO21 / TAXMAP_RASTER), then click on the Show Layer button; repeat for the land parcel centroids layer (TAXCENT / CENTROIDS). (If these layers are absent, the cursor's position was geographically incorrect for one of the mouse clicks; either start over or consult the later section on the HyperIndex Navigator and locate the Berlin NE digital ortho quarter quad.)


land parcel centroid

Viewing tables

Choosing to Examine Attributes opens the Element Selection window and changes the active tool in the view window from the HyperIndex tool to the Select tool. Don't be intimidated by the Element Selection window. The scrolling portion of the window is merely a repeat of the Layer Controls window with icon buttons added. Some of these icon buttons expand the level of detail shown. For example, you can display detailed land ownership information about any parcel with just a few mouse clicks.

ExAttrMenu choose Attributes from the Examine menu.
scroll to the bottom of the layers list in the Element Selection window
click on the TAXCENT / CENTROIDS layer icon Vector Layer
click on the Show Tables icon Show Table
click on the view Table icon for TABLE View Table
choose Single Record from the Table menu in the CENTROIDS / PointData / Table view
click on any of the centroids that are in the view of the layers



The HyperIndex® Navigator Show HyperIndex Navigator


Once you reach the map quadrangle level, the Navigator window is quite useful. It lets you click a button and move to the nearest adjacent quadrangles or other reference layers at the same level, such as the scanned photographs of historic locations. If an arrow is dimmed, there is nothing in that direction. The name of the reference layer available in the direction of any active arrow is provided as a ToolTip. Once you click on the Show HyperIndex Navigator icon, the window will be open whenever the HyperIndex tool is active (until you click on the Show HyperIndex Navigator icon again to close it).

Measurement tools Measure
Six different tools are provided for making measurements on any view.

Printing Print Snapshot

Snapshot printing is provided to print any view on letter size paper. Click on the Print Snapshot icon on the toolbar. The Page Setup window may open the first time you print if your Windows printer setup is incomplete. Printing may be slow with your Windows print driver. The atlas contains text files you can print to better understand the purpose and operation of the atlas. There are also many detailed metadata files for information about the data.

If you get a blank page when printing, change your printer spooling setup in Windows from the default to either of the other two options.

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