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Symbolize crime locations

To begin your crime analysis, you'll create a map of crimes in the past month using layers from the Lincoln Police Department. First, you'll familiarize yourself with the data. Then, you'll symbolize the map so that the data is more clear and understandable at a glance. Lastly, you'll label some key geographic features for future reference.

Create a map

First, you'll open a map and add layers that represent crimes, police stations, and a township boundary in the Midwestern American city of Lincoln, Nebraska.

  1. Sign in to your ArcGIS organizational account.
    Note:

    If you don't have an organizational account, you can sign up for an ArcGIS free trial.

  2. At the top of your organization home page, click Map.

    Map link

    If you're in a new session, a new map opens with a basemap, which is the global reference information that provides geographic context to the data layers that you'll add.

    Note:

    If an existing map opens instead, click New Map in the upper right corner of the page, and choose Create New Map.

  3. On the ribbon, click Add and choose Search for Layers.

    Search for Layers

    You'll search ArcGIS Online for layers that include data for Lincoln, Nebraska. You'll also limit the search results to layers owned by the Learn_ArcGIS account.

  4. In the Search for layers pane, click My Content and choose ArcGIS Online.
  5. For Search for layers, type Lincoln owner:Learn_ArcGIS and press Enter.

    Results

    The search returns four results.

  6. In the list of results, and in the following order, click Add next to each layer to add them to the map:
    • Lincoln Crime
    • Lincoln Municipal Districts
    • Lincoln Police Stations
    • Lincoln City Boundaries

    Map of Lincoln, Nebraska

    The map zooms to Lincoln, Nebraska, and four new layers appear in the map. The thick outline is the city boundary, and the transparent pink polygons are municipal districts. The large black points are the location of police stations. The smaller black points are the locations of crimes that occurred during the past month, but they are somewhat difficult to see because they are obscured by the districts layer. You'll change the drawing order of the map layers.

  7. Click the Back button.

    Back button

  8. Click the Content button to open the Contents pane, which lists all the layers within the map.
  9. Point to the Lincoln Crime layer, click the vertical ellipsis next to the layer name and drag the layer above the districts layer.

    Reorder Contents pane layers

    The crimes layer now appears above districts on the map, and the symbols are easier to see.

  10. If necessary, move the other layers so they appear in the following order in the Contents pane:
    • Lincoln City Boundaries
    • Lincoln Police Stations
    • Lincoln Crime
    • Lincoln Municipal Districts

    All the layer names don't need to include the word Lincoln, so you'll also rename the layers.

  11. Point to the Lincoln City Boundaries layer name, click the More Options button, and choose Rename.

    Rename

  12. In the Rename window, change the layer name to Lincoln.
  13. Rename the other layers:

    • Change Lincoln Police Stations to Stations.
    • Change Lincoln Crime to Crime.
    • Change Lincoln Municipal Districts to Districts.

    This lesson assumes that the default basemap is Topographic, but your organization may use a different default. The Topographic basemap emphasizes parks, landmarks, and physiographic features. Instead, you'll use the Streets basemap, which emphasizes roads and other urban features.

  14. Click Basemap and select Streets.

    Streets

    The basemap updates in your map.

    Updated map

    The police stations are somewhat difficult to see because they have a similar symbol as the crimes. The check boxes next to each layer indicate whether the layer is visible on the map. Currently, all of the layers are checked, so you can see them on the map.

  15. Uncheck the Crime layer to turn it off.

    Lincoln map with the Crime layer turned off

    With the Crime layer turned off, the Stations layer is much easier to see on the map. The police stations are mostly near the center of the city, although some are closer to the city boundaries.

  16. Turn the Crime layer back on.

    To better view both crimes and police stations at the same time, you'll change the symbology of the layers. Before you do that, you'll save your map.

  17. On the ribbon above the map, click Save and choose Save.

    The Save Map window opens. In this window, you provide a name for your map, set some of its metadata, and choose where to save it.

  18. For the title, type Lincoln Crime Analysis.
  19. Specify some tags, such as crime, Lincoln, Nebraska, heatmaps, drive-time.
  20. For the summary, type Map showing the locations of police stations and crimes in Lincoln, Nebraska.
  21. Choose the folder where you want to save the map.
    Note:

    If you're new to ArcGIS, you may only have one folder available. You can create new folders in My Content, although it's recommended that you save the map first to make sure you don't lose any data.

    Save Map window

  22. Click Save Map.

    The name of the map appears above the ribbon, indicating that the map was saved successfully.

Examine the data

Before you update the map's symbology, it's important to learn about the attributes of the data. Most layers have tables, which contain additional information, or attributes, about the features on the map. These attributes can be used for symbology and analysis.

  1. In the Contents pane, point to the Crime layer and click the Show Table button.

    Show Table button for the Crime layer

    The Crime layer's table opens.

    Table for the Crime layer

    At the top of the table is the total number of features in the layer: 1,025. The table's columns contain the attributes. This layer has four attributes: Day (the day on which the crime was committed), Address (the location of the crime), Offense (the type of crime), and District (the municipal district in which the crime took place).

  2. Click the first row of attributes to select it.

    Selected attribute

    The feature on the map that contains the selected attribute data is also selected (indicated by a blue square around the feature). The selected point represents a larceny that was committed on Friday at 4717 Union Hill Road.

  3. Close the table.

    The selection is cancelled, and the feature on the map is no longer highlighted.

  4. Optionally, open the tables for the other layers.

    Most of the remaining layers contain less attribute information than the Crimes layer. The Stations layer includes the address of each station, while the Districts layer numbers each district from 1 to 5. The Lincoln layer contains a variety of attributes, including government identification numbers and the city population, but this information will likely not be useful to your crime analysis.

  5. Close any open tables.

Change the symbology

Now that you're more familiar with the data, you'll change the symbology so that each layer is more understandable on the map. First, you'll make the Stations layer more distinct from the Crimes layer. Then, you'll change the Districts layer so that each district has its own symbol, making them easier to distinguish at a glance.

  1. In the Contents pane, point to the Stations layer and click the Change Style button.

    Change Style button for the Stations layer

    The Change Style pane opens. You can choose to symbolize the layer by an attribute, a single symbol, or a heat map. Symbolizing by an attribute will give each feature in the layer a different symbol depending on its attribute data. A heat map symbolizes the layer based on feature density. You only really want to be able to distinguish the location of police stations on the map, so you'll symbolize the layer with a single symbol.

  2. For Select a drawing style, under Location (Single symbol), click Options.

    Options for single symbol

    The pane changes to show the options for the Stations symbol.

  3. Under Showing Location Only, click Symbols.

    Symbols for the Stations layer

    A window appears with additional symbology options, including options to change the symbol's shape and color. Instead of the black circle symbol, you'll choose a symbol that's more clearly indicative of a police station.

  4. Click the menu of categories and choose Safety Health.

    Safety Health category

    The list of symbols changes. The Safety Health category contains many symbols that represent public services, including the police.

  5. In the list of symbols, click the blue police badge symbol.

    Blue badge symbol

    You can also change the size of the symbol, but the default size is acceptable.

  6. Click OK to apply the symbology to the map.

    Blue badge symbols on the map

    The symbols look good, so you'll confirm the changes.

  7. At the bottom of the Change Style pane, click OK. Click Done.

    Next, you'll change the symbology for the Districts layer. Currently, it's difficult to distinguish the different districts from one another. Because the districts are the primary subdivision of the city, you'll give each one a unique symbol so that you can distinguish them at a glance.

  8. In the Contents pane, point to the Districts layer and click the Change Style button.

    To give each district a unique symbol, you'll symbolize based on an attribute. As mentioned earlier, the Districts layer has only one attribute, which numbers each district from 1 to 5.

  9. For Choose an attribute to show, choose Districts.

    Choose an attribute to show

    The list of available drawing styles changes. In addition to Location (Single symbol), you can now symbolize by Counts and Amounts (Size), Counts and Amounts (Color), and Types (Unique symbols). The Counts and Amounts drawing styles are best used for attribute data that represents a numeric quantity. Although the Districts attribute does contain numeric data, the numbers are not quantities. Instead, the numbers are names: District 1, District 2, and so on. Because the attribute you chose contains qualitative data, instead of quantitative data, you'll choose the Types (Unique symbols) drawing style, which is best for names and categories.

  10. For Select a drawing style, under Types (Unique symbols), click Select.

    Select Types (Unique symbols)

    When you select the drawing style, the map changes to display each district with a unique symbol.

    Lincoln map with the Districts layer symbolized

    The default colors for the districts were chosen by the smart mapping capability, which coordinates colors with the current basemap. The default colors are good, so you won't change them. However, you'll increase the layer's transparency to better see the features on the basemap.

  11. In the Change Style pane, under Types (Unique symbols), click Options.
  12. For Transparency, drag the slider to 50%.

    Transparency for the Districts layer

    The transparency on the map changes automatically.

    Lincoln map with transparency

    The distinctions between each district are clear, and the districts don't obscure other information on the map.

  13. At the bottom of the Change Style pane, click OK. Click Done.

Label the features

Finally, you'll label each district with its number so you can distinguish one district from another.

  1. In the Contents pane, point to the Districts layer, click the More Options button, and choose Manage Labels.

    The Label Features pane appears. You can change the label's text and appearance. You'll specify the label's text to display the Districts attribute for each feature.

  2. For Text, choose Districts.

    The labels appear on the map, but they are small, black, and difficult to see, especially when surrounded by the black crime points. You'll change the labels to be larger and more prominent compared to the map's symbology.

  3. Change the label text size to 28. Change the label color to white.

    Label size and color

    The labels now appear large and bright on the map. However, some of the labels still blend a little into the rest of the layers. You'll add a halo, or border, around the labels to make them stand out even more.

  4. Check the Halo box. Change the halo color to black.

    Halo options

    The changes appear automatically on the map.

    Lincoln map with labels

  5. At the bottom of the Label Features pane, click OK.
  6. Save the map.

Your map now displays its data layers much more clearly. Now that you've changed the symbology of the layers, you'll begin your analysis of the amount of crime that occurs close to police stations. In the next lesson, you'll create a five-minute drive-time area around police stations and calculate the crime percentage within that area. Doing so will allow the Lincoln Police Department to determine if their police stations provide adequate coverage of the city, or if they need to allocate more resources to officers in the field.