Creating Thematics

 

Thematic mapping is the production of maps to express information about a specific phenomenon. Examples of thematic maps include: polygons representing sectors of a city colored differently based on the crime rate of each sector; points representing cities displayed using different symbol sizes based on the population in the city, etc. In JMap, you can create thematic maps using the bound attributes of a layer. Depending on the value of their attributes, map elements will then be displayed differently. Using JMap Admin, you can create as many thematic maps as you want and you can also create many thematics using the same layer.

In JMap, there are 2 main categories of thematics: classifications and proportional quantities.

To create a thematic, press Create in the thematic section of the layer parameters.

Next you must select the type of thematic to create.

Classification

Thematics that use a classification separate map elements in a finite number of categories (also called classes), each having a specific style. When a map element part of such a thematic is displayed, it uses the style of the category it belongs to in order to render itself on the screen.

Creating a graduated style thematic

 

Graduated style thematics use a graduation of one or more visual variables to represent the elements of the different categories. Examples of such graduations include: the fill color of polygons that is graduated from white to red, the size of point symbols that is graduated from size 1 to size 5, the line width of elements that is graduated from 1 to 4, etc. In all cases, there is a finite number of categories and every element of the layer falls in one of those categories. Only a numeric attribute can be used for this type of thematic.

To create a new thematic of this type, you need to select the numeric attribute to use, define the number of categories, select the range calculation method and define the category styles.

There are several methods for calculating the ranges of values for the categories of this type of thematic. See Methods for calculating ranges for more information.

 

 

The next section allows you to define the styles of the categories. There are two possibilities: create custom range styles or use color schemes.

Custom range styles

You must define the from and to values of the style by indicating the style variables that will vary (e.g. border thickness, symbol size, fill color, etc.). The category styles are then generated by interpolation between the from and to styles. Optionally, a third style can be used to create an inflexion point. If an inflexion is defined, the generated styles will pass through the inflexion point at the specified position in percentage. The interface is different based on the element type of the layer.

 

 

Color schemes

Instead of manually defining styles, you can select a color scheme to generate the styles of the thematic's categories.

 

Creating a graduated symbols thematic

 

Graduated symbols thematics draw symbols superposed on the elements they qualify. The symbol sizes are graduated according to a finite number of categories based on a numeric attribute. The symbols can be used with any map element type. Only numeric attributes can be used for this type of thematic.

There are several methods for calculating the ranges of values for the categories of this type of thematic. See Methods for calculating ranges for more information.

The creation process is the same as for creating a graduated styles thematic.

Creating an individual values thematic

Examples of thematics using individual values classification

Individual values thematics represent all elements that have the same attribute value with the same style. This type of thematic is not using a range of values for each category but rather a specific value. The maximum number of unique different values is 512. If your layer has more different values, it will not be possible to create this type of thematic on that layer. Numeric and non numeric attributes can be used with this type of thematic.

To create a new thematic of this type, basically all you need to do is to select the attribute to use.

JMap proposes random colors for this type of thematic. You can accept the proposed set of colors or press Regenerate to generate new colors. You can also click on Color Schemes to use a predefined color scheme. When the thematic is created, each style can be manually edited.

Creating an individual custom values thematic

Individual custom values thematics are similar to individual values thematics except that you can define your own values, instead of being limited to values already present in the data. This is useful when you create thematics using a data set that does not contain all the known possible values for an attribute. When new data is later added to this data set, the new values will be handled properly by this type of thematic.

The creation process is similar to creating an individual values thematic except that you have the option to modify the list of individual values by adding, removing or modifying categories.

Proportional quantities

Proportional quantities thematics represent map elements using a continuous variation of a visual variable (e.g. symbol size, fill color, etc.) based on a numeric attribute or set of attributes.

Creating a proportional symbols thematic

 

Proportional symbols thematics draw circular symbols superposed on the center of the elements they qualify. The symbol sizes are determined by interpolation between the minimum and maximum values of the attribute. Only numeric attributes can be used for this type of thematic.

To create a new thematic of this type, you need to select the numeric attribute to use and define the from and to styles. The symbol size and color will be interpolated between the from and to values.

 

Creating a pie charts thematic

 

Pie charts thematics draw pie chart diagrams on the center of the elements they qualify. This type of thematic works with one or many numeric attributes. Each part of the diagram (piece of the pie) is associated with a different attribute. The size of the diagram is proportional to the sum of the attribute values. Only numeric attributes can be used for this type of thematic.

To create a new thematic of this type, you need to select one or more numeric attributes to use and define the chart style.

 

 

Creating a bar charts thematic

 

Bar charts thematics draw bar chart diagrams on the center of the elements they qualify. This type of thematic works with one or many numeric attributes. Each bar of the diagram is associated with a different attribute. The size of the diagram is proportional to the sum of the attribute values. Only numeric attributes can be used for this type of thematic.

The creation process is similar to creating a pie charts thematic except for the chart style interface that is slightly different.

 

Methods for calculating ranges

Several different methods can be used to calculate the ranges of values for the categories of thematics using classifications. These methods are described below.