Example: Add, Delete and Edit Thematic Formatting Intervals

This topic provides a step by step example of adding, deleting and editing intervals in the Style dialog that are used for thematic formatting.


In this example we continue using the same drawings and similar map as used in the Example: Format the Size of City Points by Population topic, with the addition of labels layers and some slight changes in the colors used in the Regions drawing.



   We open the map and click on the Cities tab of the map to make it the active drawing.



In the Style pane we click on the Fill color property for points, which brings up the thematic formatting settings assigned in the Example: Format the Size of City Points by Population topic.  This thematic format uses the Pop  field to choose the fill color based on the population of each city.   



We will manually add a new interval.   We begin by Double-cicking the cell next to the asterisk * symbol in the last row of the intervals list.  



That opens an editing box that allows us to enter a value.



We enter the value of 3000000 and then press Enter to accept the edit.



When we do a new interval boundary appears, in this case a new highest bound, with a color well that allows us to change the value of the color assigned to that bound.  We Double-click onto the color well and change the color from blue to purple.


Next, we will edit the interval bound for the row above.  



We first Double-click onto the row for 2125200 to open it for editing.



We change the value to 100000 and then we press Enter to accept the edit.  



We press Update Style to apply the changes to the drawing.



The fill colors for Cities immediately change to show the new interval ranges.   Cities that have populations over 100000 now are rendered in red fill color.


Next we will delete a bound, thus deleting an interval.



Ctrl-click on the row for the 100000 bound to select that row and then press the Delete icon in the toolbar.



The bound is deleted, thus deleting one of the intervals so that what once were two intervals, one from 50200 to 100000 and the next to 3000000 is now a single interval from 50200 to 3000000.  Press Update Style to commit the change to the drawing.  



The result is that cities such as Tours with a population over 100000 now share the same formatting as cities such as Poitiers with populations above 50200 but below 100000.


 The illustrations above do not show percentages next to the color wells.  Manifold defers computing statistics until we re-tally on small data sets or until we press the Refresh button in the intervals toolbar.   




Pressing the Refresh button in the intervals toolbar immediately displays statistics.

Interpolating for Continuous Values

Examples so far have used the Tally button with Methods such as equal intervals to group records into intervals and then assigning the same formatting to all records in that interval.   That provides a limited number of sizes or colors which can help make a display more comprehensible than if every record, that is, every object, has a different size or color.   


But sometimes we would like every object to have a different color or other characteristic that depends upon the value of a field.  That is easy to do.  The next few steps show how using the Fill color property as an example.


We begin by changing the number of Breaks to 2, which means we want a single interval, and then press the Tally button.



We change the color values to blue for the lowest value and to yellow for the highest value and then we choose a Fill rule of interpolate.  We are aiming for a continuous range of colors to be used in our display from blue to green to yellow.   We press Update Style to apply that thematic formatting to the drawing.



Well, that's not what we had in mind.   Instead of points colored in a continuous range from blue to green to yellow we have points that all seem to have the same blue color assigned to the lowest value.  Why is that?


What is going on is that the population values in our data set range from 20000 to over two million, but in France there really is only one large city, Paris, and all the other cities are much smaller.   Even the "big" cities in view in the map above like Tours or Clermont-Ferrand have populations of a mere 135000 or so.    The range of population values seen in the map above almost all fall in a range that is about one twentieth of the range from the smallest population to Paris, so the color variations are all packed into an interpolated range that is only one twentieth of the way from blue to yellow, that is, all shades of blue not far on the way from blue to blue-green, let alone all the way to yellow.  They are all so close to the starting blue color they all seem the same.


We can fix that by adding a second interval to take care of the bigger cities where having a heavyweight population of over two million at the top end will not influence the interpolation of colors we would like to have for the many smaller cities.



Using the techniques shown earlier we add a new interval bound of 100000 to which we assign a red color.


We add the new interval by double-clicking on the asterisk * row.  When we enter a value of 100000 for the interval that is lower than the higher bound of 2125200, the new 100000 interval will automatically move up between the 20000 interval and the 2125200 interval.


We press Update Style to commit the changes to the drawing.



There, that is better.   The smaller cities with less than 100000 population that occupy much of France now have their fill colors interpolated from blue to green to yellow, while the larger cities are colored in a range from yellow to red, but appear primarily yellow since their populations are so close to the yellow side of the range from 100000 to 2200000.


Old Data - The illustrations in this topic use data from the US military, which show the regions of France as they were before 1 January 2016, when a law passed in 2014 took effect that reduced the number of regions in France from 22 to 13. 


Point Styles and Pixels - When using point styles that include precisely vertical or horizontal lines, with some choices of symbol size we can encounter visual effects where some point symbols seem sharper than others when seen on a computer monitor.  That is a result of thinner lines being interpolated slightly differently for rendering on the grid of pixels that makes up the display screen.   We can deal with that easily, as discussed in the Style: Symbol Sizes and Pixels topic.

See also







Style: Drawings


Style: Labels


Style: Thematic Formatting


Style: Symbol Sizes and Pixels


Style: Overrides


Example: Change Point Style - Using new Style pane controls to change point style, either very rapidly one property at a time, or using the total Style button to compose a new style with changes to several properties at once.


Example: Style Pane Quickstart - A tutorial introduction to using the Style pane to apply color, symbology, size and rotation to areas, lines and points in drawings.


Example: Format a Drawing using the Style Pane - In this example we provide a first, step by step look at how to format areas in a drawing using the Style pane.  We can specify the same formatting for all areas or use a field to automatically set formatting, a process usually known as thematic formatting.


Example: Format the Size of City Points by Population - A common GIS task is to format the size of points in a drawing based on some value.  For example, the size of points that represent cities might be formatted based on the value of the city's population, with cities that have larger populations being marked by larger point icons.  This is an example of thematic formatting and is easy to do using the Style pane.


Example: Style Properties in the mfd_meta Table - Style properties for drawings such as colors for areas are stored in human readable JSON values as properties in the mfd_meta system table.   This example shows how we can copy formatting from one drawing to another by simply copying values between records in the mfd_meta table.


Example: Formatting Tricks - The visualization capabilities of Manifold using Style can be exploited to provide many visual effects.  This topic provides some examples of how to use Style in unexpected ways to create a range of more elaborate effects.


Example: How Not to Format a Drawing -  When using Style to format a drawing it is a really bad idea to use the same color for objects that is used for the background color.    It can also be a bad idea to use transparent color.   This topic illustrates why.