Thematic mapping is a powerfull way to analyze and visualize dynamic data. It is a process of enhancing geographic map according to a selected theme. Themes represent the custom data read from data sources with shapes of colors, fill patterns, or symbol shapes.
Davisor Chart Thematic Mapping extension provides a map chart factory that can be used
to illustrate objects that have a geographical area representation.
For example, the borders of European countries can be drawn with the map chart.
The capabilities of the map chart are not limited to just drawing the borders of areas but much more information can be illustrated.
Mandatory channels: one object channel.
Optional channels: other object channels, alt, color, label, paint, shape, stroke, url, value channels.
Note that the channel in which the object to be drawn are given is object, not value.
Representing all information necessary for drawing the borders of a country, for example, as a value is cumbersome. Drawing of the borders requires many lines that are of varying length and at varying angles. Specifying such instructions is error-prone. Therefore, the instructions for drawing objects are stored in property files from which the instructions, once those are once written, can be used repeatedly. The instructions from property files can be fetched with an id that is unique for the property file.
The values in the value channel can be used directly by different charts. For determining which instructions to use from a property file, an id has to be supplied. Such an id is not directly usable by charts. Therefore, a value channel is not a correct channel to use for specifying ids. For specifying ids, which are used for fetching instructions or rather objects from a property file, an object channel is used.
The property files that the map chart should use are identified with a namespace attribute in <attributes/> tag. For example, if the namespace attribute were defined as:
<attributes chartType="map" namespace="USA_2001">the property files that the map chart would use would be:
The "USA_2001_shapes.properties" file has instructions for drawing shapes, which represent areas, into a map chart. The instructions for each shape are given in the format of Scalable Vector Graphics (SVG). The syntax of the SVG path is described in detail in SVG1.1 path specification. Each shape is identified with an id.
The property file "USA_2001.properties" is optional. It can contain information for objects given in object channel as described in Maps chapter. As an example, consider the drawing of a state named Delaware in the United States.
The data for drawing Delaware is given simply with:
<data>
<column dataType="TEXT" id="#0" type="object">
<e>DE</e>
</column>
</data>
|
|
| State Delaware. |
The "USA_2001.properties" file has the following information about Delaware:
DE.name property. Showing of the name is accomplished with:
<plot font="Arial-18-plain"
valueFormat="{.name}"
valuePaint="white-50%"/>
The meaning of the value of the DE.shapeRef property can be found by examing the "USA_2001.properties" file. The following information can be found from the file:
<data>
<column dataType="TEXT" id="#0" type="object">
<e>10001</e>
<e>10003</e>
<e>10005</e>
</column>
</data>
|
| Counties of Delaware. |
These counties have also the following properties:
Okay, the shape paths of the counties are used for drawing of the counties. However, there is no shape path defined for the Delaware state! What shape is used for drawing the state? Because the shape of the state is combined from the shapes of the counties, there is no need to separately specify a shape path for the state. The outline border of the combined counties is used for the shape of the state.
It is possible to draw both the counties and the state to the same map. Furthermore, the border of the state can be made to be different from the borders of the counties. For example, by defining the data and attributes like this:
<data>
<column dataType="TEXT" id="#0" type="object">
<e>10001</e>
<e>10003</e>
<e>10005</e>
</column>
<column dataType="TEXT" id="#02" type="object">
<e>DE</e>
</column>
</data>
...
<plot stroke="10" ...>
<series idRef="#0"
lineAlignment="inside"
lineColor="red"
paint="lightblue"/>
<series idRef="#02" lineAlignment="outside"/>
</plot>
|
| The state of Delaware and it's counties. |
Various information related to the drawn areas can be shown with thematic mapping. The areas to be drawn are given in object channel. The values of the related information are given with other channels. For example, the related values can be given with paint or shape channels. If the values are given in a paint or shape channel, the information is illustrated with paints or shapes, respectively.
As an example from thematic mapping, consider the usage of electricity in the counties of Delaware. In the following example, fictitious values that represent the export of electricity are given to the counties.
|
| The amount of exported electricity. |
The data from a small example as above can easily be analyzed by other means but thematic mapping. However, when the amount of data points get bigger, thematic mapping can help in finding out important facts. As an example, consider the usage of electricity in most of the states as depicted in the following example. The values are again fictitious.
|
| The amount of exported electricity. |
Description of visualization scales.
Due to the fact that HTML imagemap areas cannot contain holes, you may not be able to click regions inside another region. To get the inner region clickable, provide it in your data AFTER the outer region.