Fade to white?
September 03 2008 |
During the one minute cartographer session at the 2008 ESRI conference, you mentioned a technique called fade to white. Can you explain again how that is done?
Mapping Center Answer:
Creating the “fade to white” effect
Note -- this only works on white backgrounds!
Buffer vignettes are a great way to symbolize the interface between two areas. They are often used to show the land-water interface by gradually fading the blue water color into white. You can also use them to fade the map out into a white background. These types of vignettes are created using buffers that are symbolized in a special way.
Create buffers for the vignette
- In ArcToolbox, click Analysis Tools.
- Click Proximity toolset.
- Click Multiple Ring Buffer.
- Double click the tool.
- Set the input features that constitute the perimeter of your study area.
- Call the output feature class bufferVignette.
- To make 16 rings that decrease in size from 5 miles to one mile, enter these distances in ascending order: 5, 9, 13, 16, 19, 22, 24, 26, 28, 30, 31, 32, 33, 34, 35, 36. The last buffer is used to fill in the rest of the data frame as you will see below. Use the Plus sign to add each new number. (The numbers you use are scale dependent—it’s really more a matter of measuring so use the Measure tool to determine the width of the buffer and then divide that distance using the proportions shown above as an example.)
- Make sure you set the Buffer units to Miles.
- Click OK.
- Rename the new layer Buffer Vignette in the Table of Contents and move it below the State Outline and above the County Outline.
Adding fields to a table
- Right-click the Buffer Vignette layer in the Table of Contents and click Open Attribute Table.
- Click Options in the table to which you want to add a field.
- Click Add Field.
- Type the name of the field. Use Xpar. This is the abbreviation for “transparency”.
- Click the Type dropdown arrow and click the field type. Use long integer.
- Click OK.
Calculating the transparency level
- Right-click the layer or table you want to edit and click Open Attribute Table.
- Right-click the Xpar field heading that you want to make a calculation for and click Calculate Values.
- Click Yes when you see the dialog box. You can make calculations without being in an editing session; however, in that case, there is no way to undo the results.
- Use the Fields list and Functions to build a calculation expression. Enter this expression: 100-((100 * [distance])/36). This will calculate transparency values that are a function of the distance so that the buffers farther away are less transparent.
- Click Save.
- Name the calculate statement Xpar_values.cal. Click Save.
- Click OK.
Creating the universe polygon
Notice that you can see outside the extent of the last buffer. What you need to do to get rid of the rest of the image is to create one additional polygon in the buffers layer that will extend just outside the data frame. There are MANY ways to skin this cat -- here is but one. If you have others that work for you, share them with us in the Comments at the bottom.
Adding the Editor toolbar
- In ArcMap, click the View menu.
- Point to Toolbars.
- Click Editor. The toolbar is added.
Editing the buffer layer
- Click the Editor menu and click Start Editing.
- Choose the CA_buffer layer to edit it.
- Use the Zoom In tool on the Layout toolbar to zoom in closer to the data frame with the buffer in it.
- Use the Zoom In tool on the Standard toolbar to zoom in closer to the edges of the buffer layer.
Creating a polygon feature by digitizing
- Click the Current Task dropdown arrow and click Create New Feature.
- Click the Target layer dropdown arrow and click a line or polygon layer. This is the CA_buffer layer.
- Click the Tool Palette dropdown arrow and click the Sketch tool.
- Click on the map to digitize the feature's vertices. You want to create a polygon in the shape of a box with four vertices around the edge of the buffered state -- get close to the edge of the data frame, and if you get a warning that you are out of bounds, just make the box a little smaller.
- When finished, right-click anywhere on the map and click Finish Sketch. The polygon is created on your map.
Now we will make the vertices to exact locations.
Moving a vertex by specifying x,y coordinates
- Click the Current Task dropdown arrow and click Modify Feature.
- Click the Edit tool and click the polygon you just digitized.
- Click to select the vertex you want to move. Start with the one in the upper left.
- Position the pointer over the vertex until the pointer changes.
- Right-click and click Move To.
- Type the x,y coordinates where you want to move the vertex. Use coordinates that are just outside the area of display for your map.
- Right-click any part of the sketch and click Finish Sketch. The feature is reshaped.
Calculating the transparency level of the universe polygon
- In the Table of Contents, right-click the CA_Buffer layer that you want to edit and click Open Attribute Table.
- Select the records for the polygon you just digitized.
- Right-click the field heading for the Xpar field that you want to change the value for.
- Type a value to set to the field. Use 0 (that's zero!)
- Click Editor on the Editor toolbar and click Stop Editing.
Symbolizing the buffers
- Right-click the CA_Buffers layer that you want to draw with a single symbol in the Table of Contents and click Properties.
- Click the Symbology tab.
- Click Features. Because Single Symbol is the only option, ArcMap automatically selects it.
- Click the Symbol button to change the symbol. Select White.
- Click Outline color and select No color.
- Click OK on the Symbol Selector dialog box.
- Click Advanced. Click Transparency.
- Select Xpar as the field that you will use to vary the feature transparency based on field values in percent.
- Click OK.
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