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9.2 Clickable Image Maps

A common graphical device on the Web is the clickable image map. A clickable image map is a graphic that has multiple hyperlinks, and, perhaps, Java scripts, associated to a single image. Such an image allows the Web designer to associate links and dynamic actions to graphical cues.

As an example, one use of a clickable image map might be for a travel agency offering vacation packages to different exotic locations around the world. A clickable image map of the world could be constructed to contain hyperlinks cued to the location of a mouse click on the map. For example, clicking on France might send the user to another web page giving details of vacation packages, sites to see, places to stay, and restaurants to try when visiting Paris. Clicking on Venezuela would send the user to pages on Caracas, and so on.

Clickable image maps are very useful devices for the Web because they represent an alternate, graphical means of navigating to other pages. One problem, however, is that they can be difficult to construct. For each hyperlink, a region of the image must be defined that activates the link when the mouse is clicked in it. This region is defined by a polygon, which in turn is specified by a set of pairs of coordinates giving the locations of the polygon's vertices. The difficulty comes from trying to determine the coordinate values. For an image map containing many hyperlinks associated to complicated regions, the task of assembling these points can be quite arduous.

Fortunately, the ImageMap  plug-in, found in the Image:Filters/Web menu, allows you to graphically input the vertices of polygonal regions by drawing directly on the image. The plug-in also allows you to easily assign hyperlinks and Java scripts to the regions. When finished, the plug-in automatically writes the HTML file that displays the newly created image map. All the positional information about vertices for the map regions is written into this file along with the hyperlinks and references to the Java scripts associated with the regions.

The initial description of how the ImageMap plug-in works is based on the blank image shown in Figure 9.13(a).

Figure 9.13: The ImageMap Plug-in
Figure 9.13

A blank image is not terribly useful as a practical image map but is great for illustrating how the ImageMap plug-in works. Figure 9.13(b) illustrates the ImageMap dialog, which consists of three main areas. There is the Drawing Canvas, where the image that the map is being created for is shown. Because the image in Figure 9.13(a) is blank, the canvas area shows a white background. To the left of the Drawing Canvas, is the toolbar containing the selection and editing function icons. These are used to draw the outlines of regions in the image that will become the clickable zones. Finally, there is the Region List, which is located to the right of the Drawing Canvas area. This is used to organize and edit the list of drawn regions.

The ImageMap selection tools are used to define the clickable regions. The selection tool choices are rectangular, circular, and polygonal. Of the three, the polygon tool is the most general because it allows for the most complex shapes to be selected. Figure 9.14(a)

Figure 9.14: Selecting a Polygon Region
Figure 9.14

illustrates an irregular shape made with the polygon selection tool. The shape is made by clicking on the polygon selection tool button and then by clicking on points in the Drawing Canvas area. Each point becomes a new vertex of the polygon. The selection is terminated, and the polygon fully defined when the left mouse button is double-clicked.

As soon as an area like the polygon in Figure 9.14(a) has been defined, the Settings  dialog appears as shown in Figure 9.14(b). This is used to specify the hyperlink associated to the selected area. As you can see from the dialog, any valid Web link can be specified. In this example, the text has been entered as the link. In addition, informational text has been added to the Comment field at the bottom of the dialog. The Settings dialog allows the polygon to be edited and Java scripts to be associated with the selected area. These functionalities are accessed by clicking on the relevant tabs shown in the dialog.

Figure 9.15(a)

Figure 9.15: Managing the Selected Regions
Figure 9.15

shows the ImageMap dialog after several areas have been selected. The three areas are each shown in the Region List, and the active one is highlighted in blue. The editing tools can be used to modify any of the areas in the Region List. You can make a particular area active by clicking on it, you can delete the active area by clicking on the button displaying the red, X icon, and you can bring up the area's Settings dialog by clicking on the button showing the pencil icon.

As seen in Figure 9.15(a), the points of the active region are displayed as red squares. It is possible to insert, delete, or move these points. Choosing the Arrow icon from the selection tools, any point can be moved by clicking and dragging it. A point can be deleted by right-clicking it, which brings up the menu shown in Figure 9.15(b). A point can be added to a line segment by right-clicking it, which brings up the menu shown in Figure 9.15(c).

After all the desired areas have been selected and hyperlinks defined, you can save the work by clicking on the floppy disk icon or selecting the Save As function from the File menu. This brings up a dialog that allows a file name to be entered. This should be a file whose extension ends in .html or .htm.

A more realistic example of the ImageMap plug-in's use is illustrated with the image shown in Figure 9.16(a).

Figure 9.16: Map of the Southeast United States and the ImageMap Dialog
Figure 9.16

This image is a map of the south-eastern United States. Each of the ten states is designated by its two-letter abbreviation: FL for Florida, GA for Georgia, AL for Alabama, and so on. The goal is to create an image map having a separate hyperlink for each state. Figure 9.16(b) shows the ImageMap dialog with the image from Figure 9.16(a) loaded into the Drawing Canvas area. The outline of each state can easily be made using the polygon selection tool. When all the states have been delineated, and when the final result is saved it produces the following file:


<!-- #$-:Image Map file created by GIMP Imagemap Plugin -->
<!-- #$-:GIMP Imagemap Plugin by Maurits Rijk -->
<!-- #$-:Please do not edit lines starting with "#$" -->
<!-- #$VERSION:1.1 -->
<!-- #$AUTHOR:Carey Bunks -->

<AREA SHAPE="POLY" COORDS="6,91,10,178,21,183,21,195,98,195,113,144,128,
107,113,104,120,92" HREF="">

<AREA SHAPE="POLY" COORDS="21,197,21,234,32,252,22,291,49,292,69,299,75,
100,197" HREF="">

<AREA SHAPE="POLY" COORDS="119,136,172,135,174,276,140,277,132,255,85,253" 

<AREA SHAPE="POLY" COORDS="119,136,269,127,288,106,334,74,168,83,170,88,
136,93" HREF="">

<AREA SHAPE="POLY" COORDS="139,91,170,90,170,81,285,75,319,43,295,28,293,12,

<AREA SHAPE="POLY" COORDS="173,272,200,271,190,248,261,247,261,208,235,130,
170,133" HREF="">

<AREA SHAPE="POLY" COORDS="237,132,263,213,266,254,342,255,342,245,357,247,
367,207,305,139,292,135,296,126" HREF="">

<AREA SHAPE="POLY" COORDS="300,127,296,133,365,205,420,146,388,120,357,122,351,
113,317,117" HREF="">

<AREA SHAPE="POLY" COORDS="333,74,270,124,304,124,314,117,354,112,360,120,386,

<AREA SHAPE="POLY" COORDS="195,253,198,271,227,271,257,288,284,275,318,303,

As you can see, each of the areas defined in the ImageMap dialog is specified by an AREA hypertext markup tag. This tag contains the coordinates of the polygon region and the text of the associated hyperlink. The example described above can be viewed as an HTML document by clicking here. HTML files created with ImageMap can be reloaded and edited by the plug-in. Normally, this is done by reloading the original image into the GIMP, running the ImageMap plug-in on the image, and then loading the saved imagemap file using the Open command from the plug-in's File menu. Figure 9.17
Figure 9.17: The Image Map Reloaded onto a White Background
Figure 9.17

shows the result of doing this with the HTML file created for Figure 9.16. However, instead of running the ImageMap plug-in on the original map image, it is done on a blank image having the same dimensions as the map. This allows you to clearly see the loaded imagemap regions against the white background. Doing this has no practical application, but it is a nice way of illustrating the results of the example. Note that the Region List area shows that each of the 10 states has an entry. Clicking on an entry in this list highlights the region in the Drawing Canvas, as is illustrated for the state of Alabama in Figure 9.17.

As a final note, with a Web browser, you can open the HTML file created by ImageMap to verify that it is working correctly. If necessary, you can edit the HTML file directly with a text editor. Figure 9.18

Figure 9.18: Map of the Southeast United States Seen in Netscape
Figure 9.18

shows how the clickable image map for the preceding example displays in the Netscape Navigator Web browser. Notice that the mouse cursor, represented by the small left-pointing hand, is located at the lower tip of the state of Florida. The fact that the mouse cursor appears as a hand means that it is over an active HTML link, and at the bottom of the browser window you can see the associated hyperlink in the link information field.

The ImageMap plug-in has many other features. This book is not the appropriate place to cover this plug-in in detail. However, most of the features are not difficult to discover, and you should be able to determine their use with a little experimentation.

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Next: 9.3 Type Effects Up: 9. Web-Centric GIMP Previous: 9.1 Web Animations