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 ArcGIS Enterprise using a named user account.
    Note:

    If necessary, confirm that your ArcGIS Enterprise configuration is sufficient to complete these lessons.

  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 Public Safety.

    Public Safety category

    The list of symbols changes. The Public Safety 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.


Map crime proximity and density

Previously, you changed the symbology of your Lincoln Crime Analysis map to better distinguish between its various features. Next, you'll analyze the proximity of crimes to police stations and the density of crimes throughout the city. For the Lincoln Police Department to determine future resource allocation, they need to know how prepared their current resources are to fight crime. If most crime occurs near police stations, few changes may be necessary. But if a significant amount of crime occurs far away from police stations, the Lincoln Police Department will need more officers in the field.

Create drive-time areas around stations

First, you'll create a five-minute drive-time area around Lincoln's police stations. A drive-time area uses information about road networks and travel speed to determine how far someone could drive from a location within a specified time. Your analysis will determine the percentage of crime that the Lincoln Police Department can respond to within five minutes.

  1. If necessary, open your Lincoln Crime Analysis map.
  2. In the Contents pane, point to the Stations layer, and click the Perform Analysis button.

    Perform Analysis button

    The Perform Analysis pane appears. In this pane, you can choose from a variety of analysis functions to derive new information from your data. Drive-time areas are a type of proximity analysis, which determines how close features are to one another.

  3. If necessary, click Feature Analysis. Expand the Use Proximity group.

    Use Proximity analysis tools

    A list of proximity analysis tools expands.

    Note:

    To learn more about any tool, click the blue information button to the right of the tool's name.

  4. Click Create Drive-Time Areas.

    Create Drive-Time Areas tool

    The Create Drive-Time Areas tool opens. Before you run the tool, you must input several parameters, including the drive-time distance and traffic conditions.

  5. For Choose point layer to calculate drive-time areas around, confirm that Stations is chosen.

    Create Drive-Time Areas first parameter

    Next, you'll choose the time for the drive-time area. Because rapid response is critical to combat crime, you'll choose a short drive time of five minutes.

  6. For Measure, confirm that the driving time is 5 Minutes.

    Create Drive-Time Areas second parameter

    You can also choose whether to incorporate typical traffic conditions into the drive-time analysis. Emergency response vehicles can usually bypass traffic, so you'll leave traffic conditions unchecked. The next parameter specifies how drive-time areas from different points will be combined. When using a point layer with multiple points, such as the Stations layer, the Create Drive-Time Areas tool will calculate a drive-time from each point. If the points are close enough, these drive-time areas may overlap. You can choose whether to keep the drive-time areas from each station as individual features or to dissolve them into a single feature for every station. You're interested in total drive-time coverage within Lincoln, so you'll dissolve the drive-time areas.

  7. For Areas from different points, click Dissolve.

    Create Drive-Time Areas third parameter

  8. For Result layer name, change the name to Five-Minute Drive-Time from Stations. Add your name or initials to make the layer name unique in your organization.

    Create Drive-Time Areas fourth parameter

  9. Click Run Analysis.

    The tool runs and the drive-time layer is added to the map. The drive-time layer can be somewhat difficult to see due to the Districts layer. Additionally, the Stations layer is now below the drive-time layer.

  10. In the Contents pane, uncheck the Districts layer to turn it off.
  11. Point to the Stations layer. Click the vertical ellipsis next to the layer name and drag the layer above the drive-time layer.

    Reorder Contents pane layers

    The Stations layer now appears above the drive-time layer on the map.

    Lincoln map with drive-time areas

    The purple drive-time area indicates all places within five minutes of a police stations. Although the police stations only seem to have coverage of about half of the total area of Lincoln, the majority of crimes seem to occur within the drive-time area. However, the exact amount of crime that occurs outside the drive-time area is unknown.

Calculate the percentage of crimes within drive-time areas

Next, you'll calculate exactly what percentage of crime occurs close to police stations (and at the same time, how much occurs far away from them). You'll calculate this percentage using the Aggregate Points tool. This tool summarizes a set of points that falls within a specified area.

  1. In the Contents pane, point to the Crime layer, and click the Perform Analysis button.
  2. In the Perform Analysis pane, click Summarize Data.
  3. Click Aggregate Points.

    Aggregate Points tool

    The Aggregate Points tool opens. First, you'll choose the layer of points and the layer of areas. You want to know the total number of crimes that occurred within the drive-time area.

  4. For Choose layer containing points to aggregate into areas, choose Crime. For Choose layer containing aggregation areas, confirm that Five-Minute Drive-Time from Stations is chosen.

    Aggregate Points first and second parameters

    Optionally, you can choose to calculate statistics for a specific attribute field. However, when you looked at the Crime layer's table in the previous lesson, you learned that none of its attributes contained numeric data, so you'll skip this optional setting.

    You can also choose a field by which to group statistics. For instance, you could find the total amount of each type of crime (larceny, assault, and so on) within the drive-time area. You only want to determine the total percentage of crime close to stations, so you'll leave the Choose field to group by parameter unchanged.

  5. Change the result layer name to Crime Near Police Stations and add your name or initials.

    Aggregate Points fifth parameter

    Note:

    Verify that all of the data points are visible within the extent of your map; if not, uncheck Use current map extent so all data points are included in the results.

  6. Click Run Analysis.

    The tool runs and a new point layer is added to the center of the map. The layer's appearance on the map isn't important, but its attribute table contains the summary information about the crime points.

  7. In the Contents pane, point to the Crime Near Police Stations layer and click the Show Table button to open the table.

    Crime Near Police Stations table

    The first attribute field in the table is Count of Points, which contains the total number of crime points within the drive-time area: 863. When you looked at the Crime layer's table in the previous lesson, you learned that the total number of crimes was 1,025. And 863 out of 1,025 is 84.2 percent. (Your results may vary as sourced data is updated periodically.)

    Approximately four-fifths of crime in Lincoln occurs within five minutes of a police station. This coverage rate is pretty good, but a significant amount of crime occurs too far away from police stations for a fast response time. To cover these crimes, the Lincoln Police Department will have to allocate resources to officers in the field, who can patrol farther away from stations and respond quickly if a crime occurs. The amount of resources allocated must be enough to handle a fifth of all crime in the city.

  8. Close the table.
  9. In the Contents pane, uncheck the Crime Near Police Stations and Five-Minute Drive-Time from Stations layers to turn them off.

Create a heat map

A significant amount of Lincoln's total area is not within five minutes of a station, so the Lincoln Police Department must make strategic decisions about where to send their field officers. To help them, you'll create a heat map to visualize crime density and highlight areas where resources should be concentrated. A heat map is a continuous surface map that maps how a phenomena or occurrence changes across an area. Previously, you used discrete data, which depicts objects or areas with unchanging spatial characteristics (such as the location of police stations). A heat map, in particular, displays density, or where features are clustered together. You can create a heat map by changing the symbology of the Crime layer.

  1. If necessary, open your Lincoln Crime Analysis map.
  2. In the Contents pane, point to the Crime layer and click the Change Style button.
  3. For Select a drawing style, under Heat Map, click Select.

    Heat Map drawing style

    The crime points on the map change into a heat map.

    Lincoln heat map

    The symbology of the heat map indicates the density of crime in a given area. Blue areas are places where crime occurs but at a low density. Red and yellow areas are places where crime occurs at a particularly high density. Based on the heat map, the highest density of crime occurs in the center of the city, with smaller pockets of crime scattered throughout. Next, you'll compare the heat map to the drive-time area to see the densest areas of crime more than five minutes away from police stations.

  4. At the bottom of the Change Style pane, click Done.
  5. In the Contents pane, turn on the Five-Minute Drive-Time from Stations layer.

    Lincoln final map

    The police stations cover most of the dense areas of crime in the city. However, there are a few dense areas on the edge of the drive-time area where the Lincoln Police Department may want to deploy more field officers. Additionally, while the area to the left of Lincoln Airport does not have very dense amounts of crime, its far distance from any stations may necessitate resources being sent there.

  6. Save the map.

The map you made can provide the Lincoln Police Department with valuable information about where crime occurs in relation to where police stations are located. You first performed a proximity analysis to find crimes that happened more than five minutes away from a police station. Then, you created a heat map of crime density to identify areas where more resources should be allocated. The information in your map can be used for other purposes, too. For instance, you could use the Districts layer in conjunction with the crime heat map to determine resource allocation for a specific district. Or, you could filter the Crime layer to only focus on crime of a specific type, such as assault or larceny. For the purposes of this project, however, your analysis is complete.

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