Shading polygons with dots
February 23 2009 |
I came across a map of North Carolina made in 1770 recently and noticed the use of dots to shade a polygon or region. Is there a way to recreate this in ArcMap?
Mapping Center Answer:
This is similar to an effect we used to symbolize the shoreline on some of the maps in the "Historical Map Effects with ArcGIS" presentation on the Mapping Center's Other Resources page. Take a look to see what I mean.
In essence, I used the lines that were generated using a Buffer tool, then I symbolized the lines using a series of line symbols that were created using randomly places points. Here are the steps:
- For expedience, you might first want to dissolve the feature you are going to buffer – in my case, it was the shoreline for a portion of the coast in southwestern England.
- Create the buffers – if you do this using the Multiple Ring Buffer tool in ArcToolbox (in the Proximity toolset in the Analysis toolbox), you have the advantage that you can make the distance between the buffers different. For the map example you sent us, you would make the buffers nearer shore closer together than the buffers farther away. For my example, I used these distances in kilometers: 0.5, 1.0, 1.5, 2.25, 3.0, 4.0, 5.0, 6.5, 8.0. Note that with Multiple Ring Buffer tool, you can specify that you want to create Outside Polygons Only – do this if you have a land polygon that you are buffering. If you are buffering a water polygon, generate buffers on both the inside and the outside, then delete the outside polygons using the Editor.
- Then convert the polygon buffers to lines – do this using the Feature to Line tool in ArcToolbox (in the Features toolset of the Data Management toolbox) so that you end up with the buffers as lines and the lines have a “distance” attribute.
- Create a set of dotted line symbols that you will use to symbolize the various lines. Note that in the example map you attached, the dots nearer the shoreline were larger than those farther from shore. Also, note that to get the “hand-drawn” look, you want to use a line template that has irregularly spaced dots. To create the dotted lines:
- Open Style Manger and navigate to the style where you want to create the dotted lines.
- Click Line Symbols in the left pane.
- Right click and select New -> Line Symbol in the right pane.
- In the Symbol Property Editor, change the Type to a Marker Line Symbol.
- On the Marker Line tab, change the symbol to a solid circle, change the size so it is smaller (the actual size will depend on the scale of your map – play around with it), and change the color, if you want (I used a brown to create the look of an antique map.)
- Click the Template tab and then click and hold over the gray box on the template ruler. Pull the box out a ways to give yourself some room to add additional dots along the line template.
- Click to add dots along the template rule – don’t use the same spacing between all dots or it will look too regular.
- If your marker symbols are too big and coalesce along the line, increase the Interval.
- Save all your edits and get back to the Style Manger dialog.
- Now that you have one line created, simply copy and paste it (right click the line symbol in the left pane of the Style Manger and select Copy then Paste – don’t forget to change the name) and make a few modifications to alter the spacing between the dots along the line and to increase or decrease the marker symbol that is placed along the line. NOTE: I only ended up having to create 4 unique line symbols: One with larger points, one with slightly smaller points, and two with even smaller points, but these two had different spacings along the line template ruler.
- Now that you have the line symbols, you can symbolize the buffer lines. Right click the layer in the Table of Contents, click Properties, and click the Symbology tab. Show categories - > Unique Fields and make “distance” the Value Field. Click Add All Values at the bottom.
- Now simply change the symbols for the lines to use the ones you created. For my map example, I assigned the line with the largest dots along the shoreline, then the line with the second largest dots was next to that, and then I alternated the last two lines for the test of the buffered lines.
This gave me a pretty good approximation to the effect on the map you sent. You can play around with the distances between the buffers and the lines symbols to modify the results to get what you want.
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