The graduated colors symbolization method determines the range of numerical values for a given attribute, then breaks that range into a number of discrete buckets and applies a color gradient.
- [Instructor] When our geo spatial data includes numeric fields we have a couple of different ways to distinguish the relative differences between features on the map. One of these is to create classification buckets that represent a range of values and then sort the data into groups. These groups can then be symbolized using a color scale that ranges from high to low. This visualization style is called graduated colors. I like to apply this to some historic fire data from Yosemite National Park and we can find that in the databases folder for the project inside of the Yosemite geo database and then we'll find fire history.
Let's go ahead and click and drag it onto the map and I'll place it above the wilderness layer. That will apply a default randomized symbology to the fire data on our map. I'm going to turn off the wilderness layer, the hiking trails and the viewpoints so that we can focus on the fire data. To get a feel for what data is available in these fire events, go ahead and visit the data tab on the feature layer group and then choose attribute table to open up the attribute table for our fire history. The attribute table opens up on the bottom of the screen and we can scroll through to see the different attributes.
One of them that I want to focus on is acres. This is the size of the burn area for each fire. Now that we know what field from the attribute table we want to use we can go ahead and close the attribute table, then visit the appearance pane on the ribbon and from the symbology drop down menu I'm going to choose graduated colors. That'll allow us to draw quantities using graduated colors. That'll open up the symbology pane on the right side of the interface and it's already selected the field acres from the list. If you need to change which field its pulling out of the attribute table though you can just use a drop down menu and choose a different field.
Graduated colors breaks the range of data down into groups and color codes each range slightly differently. In the case of our fire history data we have fires that ranged from 791 acres, and we can see that here in the upper value of the lowest symbol, the yellow patch, and if I scroll down in the table we can see that the largest fire was 59,000 acres. We can control where the symbolization changes from one color to the next, which is called the breakpoint by changing the method in this drop down menu in the middle. There are lots of options to choose from from this list and there's just as much math behind how they divy up the numbers into groups.
Luckily there's a nice description on how each method functions in the drop down menu. I'm going to leave it set to natural breaks which is at the very top of the list which creates a nice distribution between the different color patches. We can also choose how many classifications there are. Right now it's set to five classes. Five is a good number to start with but if you try and use too many it makes the map hard to read as it gets difficult for the human eye to distinguish between one color and the next. Just like with the classification symbology you can click on the individual symbol patches down below to alter their color.
But that kind of disrupts the nature of the graduated color scheme. Instead, I'm going to press the back button and instead you'll want to try and stick with the color scheme gradients that are available from this drop down menu. You can choose from lots of different color schemes but I think the red to yellow color scheme matches our fire data pretty well so I'll leave it set to that. I do want to remove the gray outline that appears around each symbol patch and you can see how that appears here in the map. In order to affect the same property for all of these symbol patches at once, click on the more button and then come up to symbols and then across to format all symbols.
Here we can make a single change that will apply to all of the symbol patches. I'll click on the properties and then come down to outline color and change it from gray to no color. I'll press apply and then the back button and that will return me back to the main symbology page for the graduated colors theme and you can see the math is updated to remove that gray outline from each of these polygons. When I'm done I can go back to the project pane and save my work by pressing control s or pressing the save icon on the quick access toolbar.
By symbolizing map features based on their attributes relative to one another you can add a dimension to the data which helps the map tell a fuller story.
- Creating a new map project
- Adding data sources to the project
- Managing data layers on the map
- Saving a project template
- Drawing new map features
- Querying and extracting features
- Creating geoprocessing models and packages
- Modifying the look and feel of the map through symbology options
- Adding map labels
- Working with 3D scenes
- Developing a map layout
- Sharing the map and data