Map Viewer allows you to explore data in various ways through a variety of smart mapping styles. When you style map layers in Map Viewer, the nature of the data determines the default styling options. You can experiment with color ramps, line weights, transparency, symbols, and other graphic elements, and see your choices reflected immediately on the map.
The styling options described below are available for visualizing features according to time and date values.
Continuous Timeline (color)
If a layer contains date values, you can use color to view the data sequentially from new to old or before and after a key date. For example, applying a color ramp with the Before and after theme to the date attribute in the Rotterdam buildings feature layer can help you see which buildings were built or rebuilt after the Rotterdam Blitz.
See an To style dates using color to show a continuous timeline, do the following:
- Follow the first five steps of Apply a style. Choose an attribute field that contains date values.
- Click the Continuous Timeline (color) style and click Style options.
- Optionally, do any of the following:
- From the Theme drop-down menu, choose a theme for the color ramp. Each color theme can tell a different story by matching colors to data in different ways.
- Click the color ramp under Symbol style and choose a different color ramp, or change other graphic parameters such as outline width and colors, and define the applicable settings. For more information, see Use style options.
- In the Style options pane, click Invert color ramp
to invert, or flip, the colors in the color ramp. - Adjust the bounding handles along the color ramp to change how it is applied to the data. You can either drag the handle or click the date next to the handle and type a new date. Experiment with the position of the handles and use the histogram and calculated average information
to understand the distribution of the data to fine-tune the message of the map.Tip:
Click Magnify slider
to enlarge the details in the histogram. To return to the original slider positions at any time, click Reset slider positions 
. - Turn on the Show features with no values toggle button to draw locations with missing data on the map, and optionally specify a style and label to represent those values.
- Turn off the Include in legend toggle button to hide the color ramp in the legend.
- If you are mapping point symbols, you can rotate symbols based on a second numeric attribute. For example, the color of the points depicts air temperature at weather stations, while the rotation of the points depicts humidity. The default symbol is round, which doesn't depict rotation well. It is recommended that you choose a different shape. Click Rotation by attribute to rotate symbols, and specify the rotation settings.
- Click Transparency by attribute, turn on the Set transparency based on attribute values toggle button, and specify the transparency settings. You can only use this option if you have numeric or date data associated with the locations. For example, if the layer contains sales data, you can adjust the transparency of each store proportionally to its revenue.
- Click Done when you are finished customizing the style, or click Cancel to go back to the Styles pane without saving your choices.
Continuous Timeline (size)
If a layer contains date values, you can use a sequence of proportional symbols to view the dates sequentially on the map. For example, you can show where the oldest buildings in Rotterdam are located using larger symbols to represent older buildings and smaller symbols to represent newer buildings..
To style dates using proportional symbols to show a continuous timeline, do the following:
- Follow the first five steps of Apply a style. Choose an attribute field that contains date values.
- Click the Continuous Timeline (size) style and click Style options.
- Optionally, do any of the following:
- Click the symbol under Symbol style and specify the applicable settings to change the styling of proportional symbols. For more information, see Use style options.
- Click Invert size ramp to invert, or flip, the symbol size order.
Note:
By default, recent dates are drawn with larger symbols and less recent dates are drawn with smaller symbols. Clicking Invert size ramp allows you to reverse this pattern.
- Adjust the bounding handles along the histogram to change how the proportional symbols are applied to the data. You can either drag the handle or click the date next to the handle and type a new date. All values above the upper handle are drawn with the same largest symbol. Values below the lower handle are displayed with the same smallest symbol. The remaining values are drawn with a proportional sequence of sizes between the two bounds. Experiment with the position of the handles and use the histogram to see the distribution of the data to fine-tune the message of the map.
Tip:
Click Magnify slider
to enlarge the details in the histogram. Click Reset slider positions to return to the original slider positions at any time. - For Size range, keep the default size range or specify a custom range (in pixels) by adjusting the slider handles or clicking the default values and entering new ones. Keep the Adjust size automatically check box checked to optimize the symbols for the current map zoom level and automatically adjust them at other zoom levels.
- If you are mapping data associated with polygons, click the Symbol style box and adjust the fill and outline properties of the polygons. For more information, see Use style options.
Tip:
By default, polygon feature symbols in the layer—for example, county boundaries—are shown on the map under the proportional symbols. To keep this setting, leave the Show background symbol toggle button turned on and optionally customize the symbol style for the background features, such as adjusting the transparency or changing the outline color. To hide the background symbols in the layer—for example, if you don't want to see county boundaries under the proportional symbols—turn off the Show background symbol toggle button.
- Turn on the Show features with no values toggle button to draw locations with missing data on the map, and optionally specify a style and label to represent those values.
- Turn off the Include in legend toggle button to hide the size ramp in the legend.
- Click Transparency by attribute, turn on the Set transparency based on attribute values toggle button, and specify the transparency settings. You can only use this option if you have numeric or date data associated with the locations. For example, if the layer contains sales data, you can adjust the transparency of each store proportional to its revenue.
- If you are mapping point symbols, you can rotate symbols based on a numeric or date attribute. For example, the color of the points depicts air temperature at weather stations, while the rotation of the points depicts humidity. The default symbol is round, which doesn't depict rotation well. It is recommended that you choose a different shape. Click Rotation by attribute to rotate symbols, and specify the rotation settings.
- Click Done when you are finished customizing the style, or click Cancel to go back to the Styles pane without saving your choices.
Age (color)
If a layer contains date or time values, you can use color to represent the age of features. Age reflects the length of time (in seconds, minutes, hours, days, months, or years) from a start date or time to an end date or time. For example, you can use this style to show how long it took first responders to arrive at the scene of medical emergencies based on the time of the incident alarm (start time) and the time the responder arrived (end time).
To style dates using color to represent age, do the following:
- Follow the first five steps of Apply a style. Choose an attribute field that contains date values.
- Click the Age (color) style and click Style options.
- In the To section, do one of the following to specify an end date:
- Click Field to use the most recent date in the specified date field.
- Click Custom date, click the date box, and choose a custom date.
- Optionally, click Flip From and To to switch the start date to the end date.
- From the Units drop-down menu, select the time units.
- Optionally, do any of the following:
- From the Theme drop-down menu, choose a theme for the color ramp. Each color theme option can tell a different story by matching colors to the data in different ways.
- Click the color ramp under Symbol style to choose a different color ramp, or to change other graphic parameters such as outline width and colors, and define the appropriate settings. For more information, see Use style options.
- In the Style options pane, click Invert color ramp to invert, or flip, the colors in the color ramp.
- Adjust the bounding handles along the color ramp to change how the color ramp is applied to the data. You can either drag the handle or click the number next to the handle and type a precise value. Experiment with the position of the handles and use the histogram and calculated average information to understand the distribution of the data to fine-tune the message of the map.
Tip:
Click Magnify slider
to enlarge the details in the histogram. Click Reset slider positions to go back to the original slider positions at any time. - Turn on the Show features with no values toggle button to draw locations with missing data on the map, and optionally specify a style and label to represent those values.
- Turn off the Include in legend toggle button to hide the size ramp in the legend.
- Click Transparency by attribute, turn on the Set transparency based on attribute values toggle button, and specify the transparency settings. You can only use this option if you have numeric or date data associated with the locations. For example, if the layer contains sales data, you can adjust the transparency of each store proportional to its revenue.
- If you are mapping point symbols, you can rotate symbols based on a numeric or date attribute. For example, the color of the points depicts air temperature at weather stations, while the rotation of the points depicts humidity. The default symbol is round, which doesn't depict rotation well. It is recommended that you choose a different shape. Click Rotation by attribute to rotate symbols, and specify the rotation settings.
- Click Done when you are finished customizing the style, or click Cancel to go back to the Styles pane without saving your choices.
Age (size)
If a layer contains date or time values, you can use a sequence of proportional symbols to view the age of features. Age reflects the length of time (in seconds, minutes, hours, days, months, or years) from a start date or time to an end date or time. For example, to show the age of code violations from complaint date to compliance date, you can show violations that are less than 30 days old with a small symbol and use increasingly larger symbols for violations that are closer to 90 days old.
To style dates using proportional symbols to represent age, do the following:
- Follow the first five steps of Apply a style. Choose an attribute field that contains date values.
- Click the Age (size) style and click Style options.
- In the To section, do one of the following to specify an end date:
- Click Field to use the most recent date in the specified date field.
- Click Custom date, click the date box, and choose a custom date.
- Optionally, click Flip From and To to switch the start date to the end date.
- From the Units drop-down menu, select the time units.
- Optionally, do any of the following:
- Click the symbol under Symbol style and change the settings to change the styling of proportional symbols. For more information, see Use style options.
- Click Invert size ramp to invert, or flip, the symbol size order.
Note:
Older features are drawn with larger symbols and younger features are drawn with smaller symbols by default. Inverting the symbol size order allows you to reverse this pattern.
- Adjust the bounding handles along the histogram to change how the proportional symbols are applied to the data. You can either drag the handle or click the date next to the handle and type a new date. All values above the upper handle are drawn with the same largest symbol. Values below the lower handle are drawn with the same smallest symbol. The remaining values are drawn with a proportional sequence of sizes between the two bounds. Experiment with the position of the handles and use the histogram to see the distribution of the data to fine-tune the message of the map.
Tip:
Click Magnify slider
to enlarge the details in the histogram. Click Reset slider positions to return to the original slider positions at any time. - For Size range, keep the default size range or specify a custom range (in pixels) by adjusting the slider handles or clicking the default values and entering new values. Keep the Adjust size automatically check box checked to optimize the symbols for the current map zoom level and automatically adjust them at other zoom levels.
- If you are mapping data associated with polygons, click the symbol under Symbol style and adjust the fill and outline properties of the polygons. For more information, see Use style options.
Tip:
By default, polygon feature symbols in the layer—for example, census tract boundaries—are shown on the map under the proportional symbols. To keep this setting, leave the Show background symbol toggle button turned on and optionally customize the symbol style for the background features, such as adjusting the transparency or changing the outline color. Turn off the Show background symbol toggle button to hide the background symbols in the layer—for example, if you don't want to see census tract boundaries under the proportional symbols.
- Turn on the Show features with no values toggle button to draw locations with missing data on the map, and optionally specify a style and label to represent those values.
- Turn off the Include in legend toggle button to hide the size ramp in the legend.
- Click Transparency by attribute, turn on the Set transparency based on attribute values toggle button, and specify the transparency settings. You can only use this option if you have numeric or date data associated with the locations. For example, if the layer contains sales data, you can adjust the transparency of each store proportional to its revenue.
- If you are mapping point symbols, you can rotate symbols based on a numeric or date attribute. For example, the color of the points depicts air temperature at weather stations, while the rotation of the points depicts humidity. The default symbol is round, which doesn't depict rotation well. It is recommended that you choose a different shape. Click Rotation by attribute to rotate symbols, and specify the rotation settings.
- Click Done when you are finished customizing the style, or click Cancel to go back to the Styles pane without saving your choices.
Discrete Time Periods (categories)
If you have date or time attributes in a layer, you can show various categories representing discrete time periods. For example, you can use different colors to represent the installation dates of smoke alarms in a given year.
To style data using discrete time periods, do the following:
- Follow the first five steps of Apply a style. Choose an attribute that contains date values.
Note:
Supported date field types include the following:
- Date
- Date only
To learn more about supported field types, see Date and time fields in ArcGIS Online.
- Click Discrete Time Periods (categories) and click Style options.
- Choose and apply options
- Optionally, do any of the following:
- Click the symbol under Symbol style to change all the map symbols at once, and specify the symbol options, such as a different color ramp or fill transparency. For more information, see Use style options.
- Turn on the Display features by value order toggle button to set the display order of overlapping features on the map based on the order of categories shown in the Style options pane and legend. If you turn on this option, overlapping features in categories that are higher in the list are drawn on top of features in categories that are lower in the list.
- Click the colored symbol next to each category in the list to customize categories individually. Available styling options for each kind of symbol are shown depending on whether the data is points, lines, or areas. For example, if the data is points, you can change the symbol shape, fill color, and outline.
- Drag a category up or down in the list to reorder the categories in the legend individually. To reorder multiple categories, check the box next to each category and click Move up or Move down to change their position in the group. This order also affects the feature display order if you turned on the Display features by value order toggle button.
- Group the categories into subcategories to add detail or context to the map legend.
- Include fewer than 10 categories in a layer for best visualization; more than 10 are difficult to distinguish by color alone. If you include more than 10, only the 10 with the highest counts are shown. The remaining are automatically grouped into the Other category. If the counts of the features can't be determined, the first 9 categories are listed individually in alphabetical order, and the rest are grouped in the Other category. To move one or more observations out of the Other list and into a main group, check the box next to each category, click Move to group, and select the group to which the observation will be moved. To hide features in the Other category, uncheck the box. To show them, leave the box checked.
- Click Options
next to the group name and do any of the following: - Click Add value to add a new value to the group.
- Click Change group colors to change the group color ramp.
- Click Select all values to select all values in the group. Click Clear selection to clear the category selection.
- Click Move up or Move down to reorder the group in the group list.
- Click the color chip next to the category name to adjust the transparency applied to an individual category. Click Transparency by attribute to adjust the transparency of unique locations per feature, and specify the transparency settings. You can only use this option if you have numeric data associated with the locations. For example, if the layer contains restaurant sales data, you can style the data according to the type of restaurant and adjust the transparency of each category proportional to its annual sales.
- Manually add a category for values that do not yet exist in the data.
- Merge multiple categories into one category represented by a single symbol.
- If you are mapping point symbols, you can rotate symbols based on a numeric attribute. For example, the color of the points depicts air temperature at weather stations, while the rotation of the points depicts humidity. The default symbol is round, which doesn't depict rotation well. It is recommended that you choose a different shape. Click Rotation by attribute to rotate symbols, and specify the rotation settings.
- Click Done when you are finished customizing the style, or click Cancel to go back to the Styles pane without saving your choices.
Group the categories
When styling a layer to show categorical data, you can organize the categories into groups to add detail or context to the map legend. For example, if the map shows crimes by type—arson, assault, theft, burglary, and so on—you can organize the crime categories into groups such as violent crimes and nonviolent crimes.
To create category groups, do the following:
- Check the box next to the category or categories you want to select and click New group.
A new group is created with the category in it. The category list and legend update to show two groups.
- Click the temporary title for the new group, type a new title, and press Enter.
- Repeat the previous step to give the other group a title.
- Drag other categories into the new group, or check the box next to each category to select multiple categories, and click Move to group.
- Repeat the previous steps to create additional groups.
- To revert the category list to a single group or remove groups, drag each category out of the group you want to remove. Alternatively, check the box next to each category to select and move multiple categories.
Manually add a category
The Types (unique symbols) style creates categories based on existing values in the data. However, you can also manually add categories for values that do not yet exist in the data. Then, when a field in the data is updated to match the value you specify, the styling for that feature automatically updates.
To manually add a category, do the following:
- Follow the first two steps of the section above to style the layer using Types (unique symbols).
- Click Options next to the group name and click Add value.
The Add value pane appears.
- Type a stored value in the Value text box.
Locations with a value for the selected field that matches the stored value appear in the new category.
Note:
Stored values must be unique. Values for manually entered categories cannot match existing values in the data or values for other manually added categories. - Optionally, if you want the category name to be different than the stored value, type a displayed value in the Label text box.
- Click Done.
The new category is added and appears in the category list.
- To delete a manually added category, drag it into the Other category. To delete multiple manually added categories at the same time, check the box next to each category, click Move to group, and choose Other.
Merge the categories
When styling a layer to show categorical data, you can merge two or more unique categories into a single category. This shortens the map legend and allows you to apply the same styling to all values that have been merged into one category. For example, if the map shows crimes by type—arson, assault, theft, burglary, and so on—you can merge the crime categories into two groups: violent crimes and nonviolent crimes.
To merge categories, do the following:
- Check the box next to the categories you want to merge and click Merge values.
The selected categories are merged into a single category shown as a comma-separated string. The category list and legend update to show a single category.
- To merge additional categories, check the box next to the merged category, select additional categories, and click Merge values.
- To revert a merged category to individual categories, check the box next to the merged category and click Separate values.
The merged category is separated into individual categories. The category list and legend update to show multiple categories.
Note:
You can merge categories from the same group or from different groups. Categories are merged with the value that has the highest position in the display order. When separated, categories remain in the group into which they were merged and appear as individual values in that group.
Color (age) and Size and Color and Size (age)
You can use these styles to show two attributes on a map using color and proportional symbols to see the age of features in the data. Age reflects the length of time (in seconds, minutes, hours, days, months, or years) from a start date or time to an end date or time. You can use the Color (age) and Size or Color and Size (age) style when you choose one date attribute and one numeric attribute or two date attributes.
One date and one numeric attribute
You can use color to show the age of features and use proportional symbols to represent the numeric attribute values. Choose the date attribute as the first attribute and the numeric attribute as the second attribute, and select the Color (age) and Size style. Alternatively, use proportional symbols to represent the age of features and use color to represent the numeric attributes by switching the order of the selected attributes and choosing the Color and Size (age) style.
For example, you can use the Color (age) and Size style to map traffic accidents, with color showing where the most recent accidents occurred based on the accident date, and proportional symbols showing how many vehicles were involved.
You can use the Color and Size (age) style when mapping storm water structures by using color to show the depth of the structures and size to show how long ago the inspections occurred based on the inspection date.
To style one date attribute and one numeric attribute to show age, do the following:
- Follow the first five steps of Apply a style.
For mapping styles that show the age of features, choose at least one attribute that contains date values. The other attribute can contain date values or numeric values.
- Repeat the previous step to select a second attribute or an Arcade expression.
The available age options depend on the order of attributes you chose and whether you chose one date attribute and one numeric attribute or two date attributes. To switch the order of the attributes, drag the second attribute to the top of the attribute list.
- Click an age style and click Style options.
- Apply the options for either of the following combinations: Age (color) and Counts and Amounts (size) or Counts and Amounts (color) and Age (size).
Two date attributes
If you choose two date attributes, you can use color or proportional symbols to show the age of features based on one of the date attributes. A continuous timeline based on the other date attribute is shown using the other rendering option (color or size). You can also choose the same date attribute twice to show both age and a continuous timeline based on that same attribute.
The Color (age) and Size style uses color to represent age based on the first date attribute and uses proportional symbols to represent dates as a continuous timeline based on the second date attribute. For example, on a map showing storm water structures, you can use color to show the age of the structures based on their construction date, and use larger symbols to emphasize structures that have older inspection dates.
The Color and Size (age) style does the opposite of Color (age) and Size, using color for the continuous timeline and proportional symbols for the age of features. For example, on a map showing city code violations, you can use color to show complaint dates as a continuous timeline from older complaints to newer complaints, and use larger symbols to emphasize code violations that have gone uncorrected for a significant amount of time.
To style two date attributes to show age, do the following:
- Follow the first five steps of Apply a style.
For mapping styles that show the age of features, choose at least one attribute that contains date values. The other attribute can contain date values or numeric values.
- Repeat the previous step to select a second attribute or an Arcade expression.
The available age options depend on the order of attributes you chose and whether you chose one date attribute and one numeric attribute or two date attributes. To switch the order of the attributes, drag the second attribute to the top of the attribute list.
- Click an age style and click Style options.
- Apply options for either of the following combinations: Age (color) and Continuous Timeline (size) or Continuous Timeline (color) and Age (size).
- Click Done when you are finished customizing the style, or click Cancel to go back to the Styles pane without saving your choices.
Types and Size (age)
If a layer contains unique values (types) and date or time values, you can use color to show various categories, or types, of features based on the unique values, and proportional symbols to show the age of features. Age reflects the length of time (in seconds, minutes, hours, days, months, or years) from a start date or time to an end date or time. For example, in a map showing sewer lines by type, you can use a different color to represent each type and different-sized symbols to show how many years ago they were installed.
To style two attributes using color to show different types and proportional symbols to show age, do the following:
- Follow the first five steps of Apply a style. Choose an attribute that contains date values.
- Repeat the previous step to select a second attribute. Choose an attribute that contains unique values.
- Click the Types and Size (age) style and click Style options.
- Apply options to Types (unique symbols) for the first attribute and Age (size) for the second attribute.
- Click Done when you are finished customizing the style, or click Cancel to go back to the Styles pane without saving your choices.