Analyze flood risk

You'll first examine your study area in Boulder County, along with some layers depicting floodways, geologic hazards, and census blocks. After visually investigating their relationships for a better understanding of the region's unique geography, you'll buffer and enrich the Floodways layer to determine areas of high flood risk.

Sign in and explore the map

To investigate the data, you first need to open the map.

  1. Open ArcGIS Online and sign in.

    ArcGIS Online

    Sign in to your ArcGIS organizational account.

    ArcGIS Enterprise

    Sign in to your ArcGIS Enterprise portal using a named user account.

    Note:

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

  2. Go to the ArcGIS Online group Identify Landslide Risk Areas in Colorado.

    The group contains a web map titled Boulder County Geologic Hazard Zones owned by Learn_ArcGIS.

  3. Click the thumbnail to open the web map.

    Map thumbnail

    The map loads in Map Viewer Classic.

    Note:
    Depending on your organizational and user settings, you may have opened Map Viewer, formerly known as Map Viewer Beta. ArcGIS Online offers two map viewers for viewing, using, and creating maps. For more information on the map viewers available, please see this FAQ.

    Now you'll make a copy of the map so you can save changes to it.

  4. On the ribbon, click Save and choose Save As.

    Save As

  5. For Title, type Boulder County Map and for Summary, type Web map displaying areas of high flood and landslide risk.

    Save Map window

  6. Click Save Map.

    The new map is saved to My Content and the new title is shown at the top of the page.

    Geologic hazard zones map

    The layer has four classifications: Major Hazard, Moderate Hazard, Moderate Constraint, and Minor Constraint. These classifications represent the likelihood of major geotechnical problems—primarily landslide potential—determined by slope (steepness of terrain), aspect (direction of slope), and soil type. Most of the Major Hazard zone in is on the western side of the county, and a thin corridor of the zone extends up the central part of the county. There are also additional Major Hazard zones scattered in the southeast.

Filter the hazards layer

For your analysis, you will only use the Major Hazard classification. In this step, you'll filter the layer to display only this classification, making visual analysis easier.

  1. In the Details pane on the left, click the Content button, if necessary.
  2. In the Contents pane, point to the Geologic Hazard Zones layer and click the Show Table button.

    Show Table button

    A table opens that shows the attributes of the layer. For this data, there is only one visible attribute: the Description field, which describes the type of hazard zone. You'll use this field to filter the layer.

    Description field

  3. Close the table.
  4. In the Contents pane, point to the Geologic Hazard Zones layer and click the Filter button.

    Filter button

    The Filter window opens, which allows you to create an expression that will limit the features a layer displays.

  5. Confirm that the first drop-down menu of the expression is set to Description, and the last drop-down menu is set to Major Hazard.

    Filter expression

    The expression is set to Description is Major Hazard, which means to show only features that are major hazards.

  6. Click Apply Filter.

    Major hazards filtered

    The map is drawn again, now with only the major hazards (in red) showing.

Investigate the census block points and floodways

While the geologic hazard data provides some insight into the landscape of Boulder County, it does not help you understand which areas are at risk in the event of a major flood or landslide. For that, you'll need to compare the high hazard zones to floodway and population layers.

  1. In the Contents pane, check the box next to the Census Block Points layer to make the layer visible.

    Boulder County census blocks layer

    A layer of points is displayed. Each point indicates the centroid of a census block, a small geographic unit used by the United States Census Bureau to track population. Larger points indicate higher populations.

    Tip:

    Learn more about United States census geography.

    A visual comparison of the census blocks to the geologic hazard zones brings some good news: the majority of the census blocks lie outside of the Major Hazard zones. This means most people (and property) will be safe when disaster strikes, right?

    Unfortunately, although landslides and other geologic hazards may begin in high geologic hazard zones, that's not necessarily where they end. Floods can carry mud and debris from the narrow canyons of the Rocky Mountains as far as a kilometer downstream and cause subsequent flooding upstream, impacting areas outside of the hazard zones.

    To expand your analysis to include the possibility of geologic hazard flow from one area to another, you'll examine the Floodways layer.

  2. Check the box next to the Floodways layer to turn the layer on.

    Boulder County floodways layer

    A layer of what looks like rivers is drawn on the map. A floodway is the channel of a stream and the areas adjoining the channel that carry floodwater downstream. They comprise part of the floodplain, which is the area that may be underwater during a major flood event.

    The floodways flow from west to northeast, draining from the high elevation of the Rocky Mountains into the relatively low elevation of the eastern plains. Unlike the Geologic Hazard Zones layer, many of the floodways intersect large population centers. During a flood, large numbers of people may be at risk.

    As previously explained, the floodways only comprise part of the floodplain. If you are to fully understand the risk involved in a flood event similar to the September 2013 flooding, you'll need to estimate the area that may be submerged during a flood.

Buffer the floodways and examine potential flood extent

Although the Federal Emergency Management Agency (FEMA) freely provides floodplain GIS data, for the instructional purposes of these lessons, you'll instead create a buffer around the Floodways layer to estimate the floodplains. While not an exact approximation of flood activity, it'll give you an idea of the stakes involved during a natural disaster.

  1. In the Contents pane, point to the Floodways layer and click the Perform Analysis button.

    Perform Analysis button

  2. Click Use Proximity and click the Create Buffers tool.

    Create Buffers tool

  3. In the Create Buffers pane, for Enter buffer size select Distance, and for Enter buffer size, type 200 and confirm Meters is selected.

    Create Buffers tool parameters

    Two hundred meters is an estimation of the flood fringe, or the area around a floodway that may become inundated with water during a major flood. The floodway and flood fringe combined make up the floodplain.

  4. For Result layer name, type Floodway Buffers and add your name or initials.
    Note:

    Layer names must be unique within your organization. Adding your name to the end of a layer is an easy way to ensure that your layer doesn't conflict with others in your organization. You can rename the layer to something simpler after it has been added to the map.

  5. Leave the Use current map extent box checked and click Run Analysis.
    Note:

    Many GIS analysis tools, including the Create Buffers tool, use the information shown in the current map extent. If you are zoomed in too far, your analysis may not include all of the relevant data.

    When the analysis is complete, a new layer is added to your map.

    Buffer layer

    At this point, you no longer need the Floodways layer.

  6. In the Contents pane, point to the Floodways layer. Click the More Options button, choose Remove, and click Yes, remove layer.

    Remove layer

  7. In the Contents pane, point to the Floodway Buffers layer. Click the More Options button and choose Rename. Remove your name or initials and click OK.

    Now that you have estimated the extent of flooding, you'll investigate a few places around Boulder County where flooding may pose a particular problem.

  8. On the ribbon, click Bookmarks and choose City of Boulder.

    City of Boulder bookmark

    The map zooms into the City of Boulder.

    City of Boulder flood risk

    Boulder is the most populous city in Boulder County as well as the seat of the county government. Several estimated floodplains run through the city, with many census block points (and thus large numbers of people) at risk. The damage here during a major flood in both property and life could be catastrophic if authorities are not properly prepared.

  9. Zoom to the Lyons bookmark.

    Town of Lyons flood risk

    Lyons is a small town nestled in the Rocky Mountains where two floodway buffers converge. Compared to Boulder, few people live here. However, the floodway buffers cover all major roads into and out of the town, including the Ute Highway and the South St. Vrain Highway. While fewer people may be at risk in this area, those who are at risk may be potentially stranded if flooding renders the roads unusable.

  10. Zoom to the Louisville bookmark.

    City of Louisville flood risk

    Louisville is a suburban community in southern Boulder County, near the Denver metropolitan area. A major floodway buffer runs along the southern fringe of the city. However, although many more people live in Louisville than in Lyons, a relatively small portion of that population lives in an area at risk of flooding. Furthermore, while some major roads are in danger of being blocked by floodwater, the floodplain mostly runs through non-vital infrastructure, such as the Coal Creek Golf Course and the Dutch Creek Park. While it is an area that may be a flood risk, at the present moment, Louisville does not appear to be a particularly high-risk area.

  11. Zoom to the Boulder County bookmark and save the map.

    You've conducted a visual analysis of the population at risk during a flood, but visual analysis can only give you a rough idea of what is really happening. In the next section, you'll conduct a more precise analysis of the at-risk population.

Enrich the floodway buffers and display the data

You'll use the Enrich Layer tool on the Floodway Buffers layer to find an estimate of how many people live in potential danger of flooding. Then, you'll configure the layer's pop-up to better display the population data.

  1. In the Contents pane, point to the Floodway Buffers layer and click the Perform Analysis button.
  2. Click Data Enrichment and click the Enrich Layer tool.
  3. In the middle of the Enrich Layer pane, click Select Variables to open the Data Browser.

    Select Variables button

    The Data Browser is a directory of all of the attributes with which you can enrich your layer.

  4. Locate and click Population.

    Population button

  5. Under Choose a Popular Variable, check 2020 Total Population (Esri).

    2020 Total Population (Esri)

    Note:

    Data Browser information is updated periodically. Your variables and values may differ. Use the most updated data available.

  6. In the upper right of the Data Browser, confirm that only one variable has been selected. Click Apply at the bottom of the window.
  7. In the Enrich Layer pane, name the result layer Enriched Floodway Buffers and add your name or initials. Uncheck Use current map extent.

    Result layer name

  8. Click Run Analysis.

    A new layer is added to your map. It looks like the original Floodway Buffers layer, but this new layer contains attribute information about population. You can find this information in the layer's table or the layer's default pop-up.

  9. Remove the layers Floodway Buffers and Census Block Points from the map.
  10. Rename Enriched Floodway Buffers to Floodway Buffers.
  11. Click one of the floodway buffers on the map to view its pop-up.

    Enriched Floodway Buffers default pop-up

    The 2020 total population is in the pop-up, but it's not displayed in the most intuitive way. The pop-up could also use some information explaining what the floodway buffer represents.

  12. Close the pop-up. In the Contents pane, point to the Floodway Buffers layer, click the More Options button and choose Configure Pop-up.
  13. In the Configure Pop-up pane, under Pop-up Title, remove the default title. Click the Add Field Name button and choose Name {Name}.

    Pop-up title

    This will display the name of the creek used as the basis of the floodway buffer.

  14. Under Pop-up Contents, click Configure Attributes.

    Configure Attributes link

    A window opens, listing the layer's attributes. Every attribute has two names: the field name, which is the layer's internal name for the attribute, and the field alias, which is the name displayed in the layer's table and pop-up.

  15. Click the field name {TOTPOP_CY} (its field alias is 2020 Total Population).

    A few options appear to the right of the fields.

  16. Change Format to 0 decimal places.

    Set decimal places

    Now when your pop-up displays the population field, it will not include any decimal places. It doesn't make sense to have a fraction of a person living somewhere.

  17. Click OK.
  18. Under Pop-up Contents, for Display, click the drop-down menu and choose A custom attribute display.

    Add button

  19. Click the Configure button.

    The Custom Attribute Display window opens. You'll create a custom attribute display using the {TOTPOP_CY} field.

  20. Copy and paste the following statement into the Custom Attribute Display window:

    A total of {TOTPOP_CY} people live in this 200-meter floodway buffer meant to estimate the area underwater during a major flood event.

  21. Highlight the text {TOTPOP_CY} and click the bold button.
    Note:

    Some internet browsers may not have the capability to format pop-ups exactly like the pop-up below. If you encounter difficulties, you can continue with the unformatted text.

    Custom Attribute Display text

  22. Click OK.
  23. In the Configure Pop-up pane, click OK.
  24. Click any of the floodway buffers on the map to confirm that your pop-up was configured correctly.

    Configured pop-up

  25. Save the map.

You've investigated the data and mapped flood risk.


Analyze landslide risk

Previously, you examined a map of Boulder County to better understand the spatial relationship between geologic hazards, floodways, and human population. You then mapped flood risk and enriched the data with population statistics. Next, you'll identify areas of landslide risk and investigate additional data variables, such as property value, that might be important to understand the total risk posed to an area.

Find floodplains that intersect geologic hazard zones

As you learned in the previous lesson, floodplains can be dangerous simply for their flooding potential. However, the danger does not end there. When floodplains intersect areas of high geologic hazard, they can become corridors for conveying mud and debris in an event known as a landslide. To find where these landslides might occur, you'll first find floodplains that cross geologic hazard zones.

  1. If necessary, open your Boulder County Map.
  2. In the Contents pane, point to the Floodway Buffers layer and click the Perform Analysis button.
  3. Click Find Locations and click the Find Existing Locations tool.
  4. In the Find Existing Locations pane, click the Add Expression button.

    You'll need to build an expression to find floodway buffers that intersect hazard zones.

  5. In the Add Expression window, create the expression Floodway_Buffers intersects Geologic Hazard Zones.

    Add Expression window

    Based on this expression, the tool will create a layer that includes only floodplains that touch the geologic hazard zones. The operation only considers filtered features, so only Major Hazard zones will be used for the analysis.

  6. Add the expression, and then change the result layer name to Potential Landslide Risk Areas, add your initials, and uncheck Use current map extent.

    Result layer name

  7. Click Run Analysis.

    Potential landslide risk areas

    A new layer is added to the map, depicting only floodway buffers that intersect Major Hazard zones. (You can check and uncheck the box next to the new layer to turn it off and on so you can see the new buffers.)

    While these floodway buffers have the potential of ferrying landslide debris downstream, it is unlikely that the entire length of the floodplain constitutes a landslide risk zone. Landslide debris can only travel so far along the relatively flat eastern plains before it comes to a stop.

  8. Click the More options button for the layer Potential Landslide Risk Areas (your name), click Rename, and remove your name or initials.
  9. Save the map.

    You'll need to conduct further analysis to represent the area where a landslide may travel along these floodplains before depositing its sediment.

Determine initiation areas

To find where landslides may travel, you first need to find where they begin—a place called the initiation area. You'll determine the initiation area by overlaying the Potential Landslide Risk Areas layer with the Geologic Hazard Zones layer to create a new layer.

  1. In the Contents pane, point to the Potential Landslide Risk Areas layer and click the Perform Analysis button.
  2. Click Manage Data and click the Overlay Layers tool.
  3. For Choose overlay layer, confirm Geologic Hazard Zones is selected. Confirm that Choose overlay method is set to Intersect.

    You want to find the exact places where floodplains come in contact with hazard zones.

  4. Name the result layer Initiation Areas and add your name or initials.
  5. Uncheck Use current map extent.

    Overlay Layers settings

  6. Click Run Analysis.

    A new layer is added to the map, although it may be difficult to see at first because its features are relatively small.

  7. To better see some of the new layer, uncheck the box next to the Potential Landslide Risk Areas layer to turn it off. Then zoom to the City of Boulder bookmark.

    Initiation areas

    The new layer represents the floodplains that intersect zones classified as a major hazard. These are areas where rock and mud from the hazard zones may funnel into the floodplains and cause a landslide.

  8. On the ribbon, click Bookmarks and click the Boulder County bookmark.
  9. Check the box next to the Potential Landslide Risk Areas layer to turn it back on.
  10. For the layer Initiation Areas (your name), click the More options button, click Rename, and remove your name or initials.
  11. Save the map.

    Now that you know where landslides begin, you can estimate how far they travel and what areas are at risk.

Derive landslide risk areas and explore the results

In this section, you'll derive new locations a certain distance from the initiation areas. These new locations will indicate areas potentially affected by a landslide—the landslide risk area.

  1. Point to the Potential Landslide Risk Areas layer and click the Perform Analysis button.
  2. Click Find Locations and click the Derive New Locations tool.
  3. Click the Add Expression button.

    As when you found the potential landslide risk areas earlier, you'll construct an expression to determine the areas you want.

  4. In the Add Expression window, create the expression Potential Landslide Risk Areas within a distance of 1 Kilometers from Initiation_Areas.

    Completed expression

    One kilometer is the distance you'll use to estimate how far a landslide may travel from the initiation area. Normally, the distance will be affected by the slope and terrain of the area over which the landslide travels, but one kilometer will suffice for the purposes of your analysis.

    This expression will derive a new layer that includes all locations in the Potential Landslide Risk Areas layer within one kilometer of the Initiation Areas layer—in other words, all the areas one kilometer upstream and downstream of where a landslide enters a floodplain.

  5. Click the Add button.
  6. For Result layer name, type Landslide Risk Areas and add your name or initials, uncheck Use current map extent, and click Run Analysis.

    Landslide risk areas

    A new layer is added to the map. The new layer depicts areas potentially affected by a landslide.

  7. Rename the new layer and removing your name or initials.
  8. Remove the Potential Landslide Risk Areas and Initiation Areas layers.

    Now that you've mapped the areas prone to landslide activity, you'll take some time to explore the map a little more closely to see how population and infrastructure may be affected by a landslide event.

  9. On the ribbon, click Bookmarks and click City of Boulder.

    City of Boulder landslide risk

    As with flood risk, the number of people in danger of landslides is relatively high in Boulder, because it is a major population center at a confluence of many floodways and geologic hazard zones. The landslide risk here is primarily downstream, meaning that people and property are under threat of being buried by landslide debris itself.

  10. Zoom to the Lyons bookmark.

    Town of Lyons landslide risk

    Only one relatively small landslide risk area threatens Lyons. However, unlike Boulder, the landslide threat here is primarily upstream rather than downstream. The people and property of Lyons aren't in danger of being buried under landslide debris as much as they are in danger of the extreme upstream flooding that might occur if a landslide dams up a floodplain. A landslide event in Lyons may exacerbate the already-severe flooding and compound problems for the people of Lyons.

  11. Zoom to the Louisville bookmark.

    City of Louisville landslide risk

    Only one landslide risk area travels through Louisville, but it is by far the largest risk area in Boulder County, due to the presence of multiple scattered geologic hazard zones throughout the city. As you discovered before, relatively few people in Louisville live in the southern fringe of the city where flooding and landslides are most likely to take place. However, the sheer size of the landslide risk area in Louisville may pose a particular difficulty for disaster preparations.

  12. Zoom to the Boulder County bookmark and save the map.

    Visual analysis only tells part of the story. You'll need to find more exact statistical data on the landslide risk areas to learn the whole of it.

Enrich the landslide risk areas

In the previous lesson, you enriched the Floodway Buffers layer with population information. You'll do the same for the Landslide Risk Areas layer, but you'll add a few additional information fields to gain an even more complete picture of what is at risk during a landslide.

  1. In the Contents pane, point to the Landslide Risk Areas layer and click the Perform Analysis button.
  2. Click Data Enrichment and choose Enrich Layer.
  3. In the Enrich Layer pane, click Select Variables.

    The Data Browser window opens. This time you are adding several layers in addition to Total Population, so you'll use the Data Browser search function to facilitate the process.

  4. In the search box in the upper left of the Data Browser window, type 2020 total population and press Enter. Check the box next to 2020 Key Demographic Indicators (Esri).

    2020 Total Population (Esri)

  5. Click the menu button in the Data Browser window to return to the main menu.

    Data Browser menu button

  6. In the search box, type total housing units and press Enter.
  7. Expand 2020 Housing Unit Time Series (Esri), and check the box next to 2019 Total Housing Units (Esri 2020).

    2019 Total Housing Units (Esri 2020)

    This statistic will indicate at-risk property.

  8. Click the menu button. In the search box, type average household income and press Enter. Check the box next to 2020 Income (Esri).

    2020 Average Household Income (Esri)

    This statistic will give you insight into the characteristics of the population at risk.

  9. Click the menu button. In the search box, type seniors and press Enter. Check the box next to 2020 Seniors (Age 65+).

    2020 Seniors (Age 65+)

    This statistic will inform you of the number of elderly people who live in an area, who may require special assistance in preparing for a flood event.

  10. Click the menu button. In the search box, type relative road density and press Enter. Check the box next to Relative Road Density (Km).

    Relative Road Density (Km)

    This statistic indicates the average total road length in an area per square kilometer, which will reveal the potential danger to road infrastructure in the landslide risk areas.

  11. Confirm that you have five selected variables.

    Five selected variables

  12. Click Apply.
  13. In the Enrich Layer pane, for Result layer name, type Enriched Landslide Risk Areas and add your name or initials, and uncheck Use current map extent.

    Result layer name

  14. Click Run Analysis.

    A Warning window appears alerting you that the selected analysis variables are from multiple hierarchies. This is because the variables were compiled at different sub-geography levels. For the purposes of this analysis, it is not a problem.

  15. Click OK to close the Warning window.

    The new layer is added to the map. It looks like the original Landslide Risk Areas layer, but this new layer contains additional attribute information. You can view this information in the layer's table or the layer's default pop-up.

  16. Remove Landslide Risk Areas from the map.
  17. Rename the Enriched Landslide Risk Areas layer to Landslide Risk Areas.
  18. Save the map.

    You've mapped both areas of flood risk and areas of landslide risk, with relevant demographic and infrastructure data. Now all you have left to do is symbolize the Landslide Risk Areas layer and configure its pop-up to more clearly relate the information to the viewer.

Symbolize the landslide risk areas and configure the pop-up

Maps aren't just about proper analysis and spatial data. You also need to be able to communicate your results to an audience. In the final section, you'll change the visual aspects of the Landslide Risk Areas layer to better convey the danger involved by using a custom icon to denote landslide risk.

  1. In the Contents pane, point to the Landslide Risk Areas layer. Click the More Options button and choose Transparency. Set Layer Transparency to 0%.
  2. In the Contents pane, point to the Landslide Risk Areas layer and click the Change Style button.

    Change Style button

  3. In the Change Style pane, for an attribute to show, choose Buffer distance in Meters.

    Buffer distance in Meters measures the size of the buffer for each feature in the Landslide Risk Areas layer. You could use any field to symbolize the layer, but this field is convenient because it only contains one value—200, the size you set your buffer distance to be in the previous lesson. This results in one symbol type.

    Normally, only point features can be symbolized with an icon. However, you can symbolize polygon features as if they were point features by using a graduated classification scheme such as size or color.

  4. Select Counts and Amounts (Size), and then click Options.

    Counts and Amounts (Size) style option

  5. In the options, click Polygons.

    Change Style Polygons

    A new window opens. You can use this window to change the background of your symbol's icon.

  6. In the color palette, choose the third yellow from the top. Set the transparency to 0%.

    Background symbol

  7. At the top of the window, click Outline. In the color palette, choose black. Uncheck the Adjust outline automatically box. Set the transparency to 50% and Line Width to 2 px.

    Background outline

  8. Click OK.
  9. In the options, click Symbols.

    Change Style Symbols

    Another window opens, allowing you to change the graduated circles symbol (as opposed to the symbol for the polygon features). Instead of using a default symbol, you'll add a custom symbol.

  10. At the top of the window, click Shape. Under the default shapes, click Use an Image.

    Shape symbol

    A text box appears.

  11. In the text box, copy and paste the following URL:

    https://learngis.maps.arcgis.com/sharing/rest/content/items/53a098f903b64daa8cf235a428b73d42/data

  12. Click the Add button next to the text box to add the image.

    Add image

    The URL belongs to a symbol specifically designed to communicate landslide risk. The default size of 12 pixels is rather small, but you currently cannot change the shape size because you are symbolizing by an attribute Buffer distance in Meters. Although Buffer distance in Meters is always the same value, by default, it is treated as though it has multiple values. You can change this by using the Classify Data option, which will allow you to set the size of the customized symbology.

  13. Click OK.
  14. In the Change Style pane, for Size, check the Classify Data box, and type 24 for Min and 24 for Max

    Classify Data and Min and Max values

    The symbol size is set to a larger size. Classify Data sets the number of classes to 1, because Buffer distance in Meters has only one value.

  15. In the Change Style pane, click Legend.
  16. For Click to edit symbol or label, click the 0 to 400 label. In the text box, highlight the text and press Spacebar to remove the label completely.

    Remove label

  17. At the bottom of the Change Style pane, click OK, and click Done.

    New symbology

    The symbols on the map change to reflect the new symbology.

    Next, you'll configure the layer's pop-up to convey only the information with which you enriched the layer.

  18. In the Contents pane, point to the Landslide Risk Areas layer. Click the More Options button and choose Configure Pop-up.
  19. For Pop-up Title, change the name to {Name} Landslide Risk Area.
  20. For Pop-up Contents, confirm that A list of field attributes is selected.

    For the Floodway Buffers pop-up, you created a custom attribute display to explain what the layer displayed. However, Landslide Risk Area is more self-explanatory, so you will configure the pop-up using a list of field attributes.

  21. Click Configure Attributes.
  22. In the Configure Attributes window, under the Display column, uncheck all of the attributes except for the last five fields with which you enriched the data:
    • 2020 Total Population
    • 2020 Average Household Income
    • 2020 Seniors (65+)
    • 2019 Total Housing Units (Esri 2020)
    • Relative Road Density
  23. For each of these attributes, except for Relative Road Density, change Format from 2 decimal places to 0 decimal places.

    Format field to 0 decimal places

    Note:

    The Relative Road Density attribute indicates an average density of roads per square kilometer. Because it is depicting an average and not a whole number, such as people or households, you can keep it formatted with two decimal places.

  24. Click OK. In the Configure Pop-up pane, click OK.
  25. Click any of the landslide risk areas on the map to confirm that you configured the pop-up correctly.

    Landslide risk areas correct pop-up

    Note:

    Keep in mind that the numbers displayed in this pop-up are merely estimates based on a generalized approximation of floodplains. However, they do provide a look at the devastating potential of flooding and landslide risk in this geologically tumultuous region.

  26. Save the map.

Over the course of this lesson, you identified the spatial relationships between different types of data both visually and analytically. You identified areas of flood and landslide risk in Boulder County and combined these areas with relevant information on demographics and infrastructure. Finally, you symbolized the data and configured pop-ups to communicate your results clearly and concisely, creating a finished web map that will inform users about the unique geologic conditions of the region.

You can find more lessons in the Learn ArcGIS Lesson Gallery.