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Visually Classifying Your Maps by Attributes

Hurricanes-result-300x187

Tired of staring at the same, drab, mess of lines and polygons? Having trouble finding the shapes you want? Mappt now has support for Thematic mapping, allowing you to style your features according to the numeric or text values in the layer’s attributes.

Here we have some geological zones. As is typical with datasets, it’s not very pretty to look at. Worse, we can’t really tell much by just glancing at it!

Geology-zones-plain

Looking at the attributes defined in the layer, we can see there is an AREA key defined.

The list of attribute values for one of the zones.

The list of attribute values for one of the zones.

Let’s say we want to easily see the zones with the smallest areas. To do this, we open the layer’s properties, then navigate to the Classifications tab. Here, we can specify how we want to classify the data. In this case, we want to find highlight the features with the smallest AREA attribute value. Let’s do some experimenting!

First, we’ll try to classify the AREA by “Distinct Values”, which will give us a class for every unique AREA value in the layer.

The Classifications screen, showing how to classify by Distinct Value.

The Classifications screen, showing how to classify by Distinct Value.

When we hit Apply, the classes are generated, and we are taken to the Class Styles tab, which shows the styling applied to each of the determined classes. In the screenshot below, we can see that there were quite a few unique values, so much so that we haven’t really achieved anything by classifying them!  Perhaps Distinct Values wasn’t such a great choice!

There are too many classes to fiddle with. We can see that classifying a numeric attribute by Distinct Value was a bad idea!

There are too many classes to fiddle with. We can see that classifying a numeric attribute by Distinct Value was a bad idea!

Let’s try again, this time using “Equal Intervals”, which instructs Mappt to classify the features into x number of classes, with x being chosen by us. So, let’s try Equal Intervals.

Let’s try that again, this time with Equal Intervals.

Let’s try that again, this time with Equal Intervals.

This will give us 5 nice classes, evenly spread across the range of values found in the AREA attribute of the features in the layer.  We can apply styling to each class, as seen in the screenshot below, where I have used the colour blue to denote the lowest-range class, and yellow for the rest.  Also note that Mappt shows us the range of each class, as well as how many feature are in it, which is handy when fine-tuning your classification parameters.

Highlighting the lower-fifth zones by area in blue.

Highlighting the lower-fifth zones by area in blue.

Closing the layer properties dialog, we can see the styling has been applied to the map. Because of the settings we choose, we have effectively highlighted, in blue, the zones that are in the lower 20% of overall zone sizes.

The smallest fifth of the zones, by area, can now easily be seen!

The smallest fifth of the zones, by area, can now easily be seen!

Using another example, here I have taken a dataset of the world’s volcanoes and classified them by elevation, using Manual Breaks defined at -4000, -2000, 0, 2000 and 4000 feet, allowing me to see which volcanoes are the highest, with increasing blue being below sea level, and increasing red being above sea level.

edit mappt layer

On the map, we can easily see which volcanoes are above or below sea level, as well as how far above or below, simply from their colour.

Volcanoes-result

One last example shows the path of hurricanes in the Atlantic, coloured by wind speed, with redder being faster.

Hurricanes-result

So in summary:

Thematic Mapping: Mappt, pretty.