Modify a raster image service
The Community Rating System (CRS) only gives discounts for specific types of open space. These areas must meet the following criteria:
- The parcel is located in the FEMA-designated 100-year floodplain.
- The parcel is open space, meaning it has no buildings, significant areas of pavement or other impervious surfaces, or dumps.
- The parcel is preserved as open space by a long-term contract from the private owner or public agency.
Because of these constraints, it's easiest to consider public lands, such as parks, and nonprofit lands, such as a church or Boy Scout camp. In many cases, it's difficult to obtain the detailed large-scale data needed for floodplain analysis. This data is more readily available at a national scale. You'll use a ArcGIS Living Atlas raster image of the United States and raster functions to prepare it for parcel-scale analysis. First, you'll filter out impervious surfaces. Then you'll clip the raster so you only have your county of interest. Finally, you'll save the ArcGIS Living Atlas raster locally and create an attribute table for it.
Download and open the project
First, you'll download and familiarize yourself with the data for your community, Georgetown County, South Carolina.
- Download the GeorgetownCo_CRS zipped folder.
- Locate the downloaded folder on your computer and unzip the file to a location you can easily find, such as the Documents folder.
The folder contains an ArcGIS Pro project file (.aprx) and a file geodatabase with the community data (.gdb).
- Double-click the CRS_Georgetown_Co.aprx file to open the project in ArcGIS Pro. If prompted, sign in using your licensed ArcGIS account.
Note:
If you don't have access to ArcGIS Pro or an ArcGIS organizational account, see options for software access.
The map contains layers for Georgetown County parcels, the county boundary, and the 100-year regulatory floodplain. It also has a basemap (Topographic), and a table, PADUS_CRS_attrib. The 100-year Floodplain layer has three zone types: A, AE, and VE. These are FEMA codes for subtypes of floodplains.
- In the Contents pane, under Standalone Tables, right-click PADUS_CRS_attrib and choose Open.
Each unique OBJECTID contains all the attributes for the Protected Areas Database of the United States (PADUS) that you'll eventually join to your parcel data. Due to the amount of records, you'll filter the national scale dataset before you join this information back to the data. Lookup tables such as this provide an efficient way to store a lot of information.
- Close the attribute table.
Modify a raster image service processing template
Now that you've seen the community data available, you'll add the Open Space Preservation Community Rating System raster image service to your map. Then, you'll use a raster processing template to filter out raster cells below a certain value. This process will remove impervious surfaces that are ineligible for the program. Then, you'll use on-the-fly processing to clip the data to your community boundary and regulatory floodplain. On the fly means that the clip is performed every time you need to access the data, rather than only once so that you must save the results. Because you're using portal data instead of locally saved data, you'll need to use raster functions instead of the similar geoprocessing tools. Once you finish clipping and modifying the raster, you'll save it to your project.
- On the ribbon, click the View tab. In the Windows group, click Catalog Pane.
The Catalog pane appears.
Note:
If you are an ArcGIS Enterprise user, on the ribbon, on the Map tab, in the Layer group, click the Add Data drop-down button. From the drop-down list, choose Data From Path. In the Add Data From Path window, for Path, copy and past the following URL and click Add: https://landscape7.arcgis.com/arcgis/services/NHDPADUSForCRS/ImageServer.
In the Contents pane, click the NHDPADUSForCRS layer twice to edit the name. Rename the layer to Open Space Preservation Community Rating System. You can skip steps 2 through 4 and continue to step 5.
- At the top of the Catalog pane, click the Portal tab and click the ArcGIS Online tab.
- In the search box, type Open Space Preservation Community Rating System. Press Enter.
- Right-click the Open Space Preservation Community Rating System imagery layer and choose Add To Current Map.
This data is from The Nature Conservancy (TNC). You can read more about it on its item page.
The raster layer draws on your map. This layer represents areas that are likely eligible for open space preservation (OSP). The layer is derived from both the PADUS and the National Hydrology Dataset (NHD), and contains the attribute max_imperv with information about the impervious surfaces within each raster cell.
- If necessary, in the Contents pane, right-click Community_Boundary and choose Zoom To Layer.
Next, you'll use the raster processing template to filter this image service to show only cells that are within a chosen threshold of impervious surface percentage. Areas that impede natural water filtration and movement are not eligible for OSP credit. These include parking lots, buildings, roads, driveways, and so on. You'll filter the national scale data based on the estimated percentage of impervious surface per grid cell. It has been shown that water quality and ecosystem health are often degraded when impervious surfaces exceed 10 percent of an area. Using this as the threshold, you'll filter the Open Space Preservation Community Rating System raster service to select only areas that likely have less than or equal to 10 percent impervious surface.
- In the Contents pane, right-click the Open Space Preservation Community Rating System layer and choose Properties.
- In the Layer Properties window, click the Processing Templates tab.
- If necessary, for Processing Template, choose OpenSpacePotential.
- In the Inputs section, for Parameter, type max_imperv. For Value, type 10. Click the Validate button to verify that your Inputs information is valid.
- Click OK.
The resulting raster shows only those cells that are estimated to have no more than 10 percent impervious surface coverage.
To qualify for OSP credit, the protected areas also must be in the regulatory floodplain. You'll clip the national raster to Georgetown County's 100-year floodplain.
- On the ribbon, click the Imagery tab. In the Analysis group, click the Raster Functions button.
The Raster Functions pane appears.
- If necessary, in the Raster Functions pane, click the System tab.
- Expand the Data Management section and click Clip.
The Clip Properties function appears.
- Click the General tab.
- For Name, type PADUS_CRS_clip (this will be the name of the output raster). For Output Pixel Type, choose 32 Bit Unsigned.
- Click the Parameters tab. For Raster, choose Open Space Preservation Community Rating System.
- If necessary, for Clipping Type, choose Outside.
Specifying Outside will remove the raster cells outside the clipping geometry. The other option is Inside, which removes the raster cells inside the clip features.
- For Clipping Geometry/Raster, choose 100-year Floodplain. Check the Use input features for clipping geometry check box.
Using input features for clipping geometry specifies that the raster will be clipped to the floodplain layer you chose. Alternatively, you can set an extent by drawing a rectangle around the area you want clipped.
- Click Create new layer.
The function may take several minutes to run. When it finishes, a temporary layer named PADUS_CRS_clip_Open Space Preservation Community Rating System is added to the map. The default name is long, so you'll rename it.
- Close the Raster Functions pane.
- In the Contents pane, click PADUS_CRS_clip_Open Space Preservation Community Rating System to select it. Click it again to make the layer name editable and type PADUS_CRS_clip.
Save the clipped raster
Now that you've filtered and clipped the national raster dataset down to a useful size, you'll save it locally for future use. Using the Export Raster tool, you'll save the raster for your area of interest as a TIFF, a compact format. Then, you'll create an attribute table for the .tif file that you'll use to join the raster with its attribute table for analysis in the next tutorial.
- In the Contents pane, uncheck Open Space Preservation Community Rating System and 100-year Floodplain to turn the layers off.
Now the new clipped layer, the county boundary, and the basemap are the only layers visible on the map. Unlike geoprocessing tools, raster functions apply an operation to a raster image on the fly, meaning that the original data is unchanged and no new dataset is created. This enables faster processing because it requires less storage and memory on your computer. However, if you remove the PADUS_CRS_clip layer from the map, you'll erase it. Because you'll need the raster later, you'll save it.
- In the Contents pane, right-click PADUS_CRS_clip, point to Data, and choose Export Raster.
The Export Raster pane appears.
- On the General tab, for Output Raster Dataset, delete the text after the last \ character and type PADUS_CRS_final.tif.
- Confirm that Output Format is set to TIFF.
- For Clipping Geometry, choose Community_Boundary.
- Check the Use input features for clipping geometry check box. If necessary, for Clipping Type, choose Outside.
- Under Raster Properties, ensure that Cell Size is set to 30 for both X and Y, and Pixel Type is set to 32 Bit Unsigned.
- For NoData value, type 2147483648, which is a value just beyond the range of actual useable values.
- Click the Settings tab. For Snap Raster, choose PADUS_CRS_clip. Click Export.
The new layer is added to the map.
- Close the Export Raster pane.
- In the Contents pane, right-click the PADUS_CRS_clip layer and choose Remove.
The data is now clipped to the extent required by FEMA. Your output is in TIFF format, which is an efficient file type but doesn't have an attribute table. To use this layer later, you'll create one.
- On the ribbon, click the Analysis tab. In the Geoprocessing group, click Tools.
The Geoprocessing pane appears.
- In the search box, type build raster. In the list of results, click Build Raster Attribute Table.
- In the Build Raster Attribute Table tool, for Input Raster, choose PADUS_CRS_final.tif and click Run.
- In the Contents pane, right-click PADUS_CRS_final.tif and choose Attribute Table.
Note:
If you can't open the attribute table, remove the PADUS_CRS_final.tif layer. In the Catalog pane, click the Project tab. Expand the Folders and CRS_GeorgetownCo_Lesson folders. Right-click PADUS_CRS_final.tif and choose Add To Current Map. This helps refresh the data.
The Value field in this attribute table represents the most common value from each cell. Later, you'll use this field to join the PADUS attribution to your parcel dataset.
- Close the attribute table.
- On the Quick Access Toolbar, click the Save button to save the project.
You've modified a raster layer to fit your community's needs. To start the CRS analysis, you filtered out impervious surfaces and clipped the national raster down to Georgetown County, South Carolina. Next, you'll perform a parcel-scale analysis on this data to determine the likely acreage of eligible open space per parcel in your community.
Calculate areas of eligible open space
Previously, you filtered the national raster based on your desired impervious surface threshold and clipped to your area of interest. Now, pursuant to the requirements of the CRS review process, you need to determine the acreage of eligible open space per parcel in your community. Since the acreage calculated also needs to be joined back to the raster data for final analysis, you'll run zonal statistics. Zonal statistics will calculate the majority statistic for a specified boundary layer, which is the same as the value attribute you gave your PADUS_CRS_final.tif layer in the previous tutorial. Once you have this information, you'll join the tables to the parcel and raster datasets.
Calculate the majority statistic
The Zonal Statistics geoprocessing tool allows you to calculate a variety of statistics, including mean and median, within a defined area. The majority statistic summarizes the most common value found in all the PADUS_CRS_final raster cells within each parcel. This field will be used later to join the parcel tables.
- If necessary, open your CRS_Georgetown_Co project.
- Reopen the Geoprocessing pane.
Note:
If you can't find the Geoprocessing pane, on the ribbon, click the Analysis tab. In the Geoprocessing group, click Tools.
- In the Geoprocessing pane, if necessary, click the Back button so you can access the search bar. In the search bar, type Zonal Statistics as Table.
- In the search results, click Zonal Statistics as Table (Image Analyst Tools) or Zonal Statistics as Table (Spatial Analyst Tools).
- For Input Raster or Feature Zone Data, choose GeorgetownCo_Parcels. For Zone Field, choose PARCEL_ID.
- For Input Value Raster, choose PADUS_CRS_final.tif.
- For Output Table, type Parcels_Zonal. Ensure that the Ignore NoData in Calculations check box is checked.
- For Statistics Type, choose Majority.
- Click Run.
If the warning message Some zones may not have been rasterized appears, ignore it. The result table is added to the Contents pane under Standalone Tables.
- In the Contents pane, right-click Parcels_Zonal and choose Open.
The table includes statistics per unique PARCEL_ID. The AREA column summarizes the area in square meters. The MAJORITY column summarizes the most common value found in the PADUS_CRS_final raster cells within each parcel. It is the same attribute as the Value field in the PADUS_CRS_final.tif attribute table. It is also is the same as the OBJECTID field in the PADUS_CRS_attrib table. You'll use this common field to join these data sources later.
Estimate open space acreage
FEMA encourages conservative estimations of OSP-eligible area per parcel. When using coarse data, you can incorporate the accuracy of the underlying data to accomplish this. In this case, 0.85 represents the measured level of interpretation accuracy for the 2011 National Land Cover Database (NLCD) Impervious Surface Estimation layer. The NLCD is the source for the max_imperv variable that you filtered the image by in the previous tutorial. Multiplying the cumulative OSP area in each parcel by this value states that you are 85 percent confident that a given parcel has at least X acres of eligible open space. Additionally, eligible OSP area per parcel is required to be reported in acres for the CRS program, so you'll convert square meters to acres.
- On the attribute table's ribbon, click Add.
The fields table appears. Here, you can change the properties of the new field.
- In the last row (the new field), for Field Name, type ACRES. For Data Type, double-click the cell and choose Double.
- On the ribbon, on the Fields tab, in the Changes group, click Save.
- Close the Fields: Parcels_Zonal table.
The ACRES field is added to the table. It is currently populated by the default null value. Next, you'll calculate the values for the field.
- In the Parcels_Zonal table, right-click the ACRES field header and choose Calculate Field.
The Calculate Field window appears.
- In the ACRES = box, type (or copy and paste) (!AREA! * 0.85) * 0.000247105.
- Click OK.
The ACRES field is ultimately what the CRS reviewer will use to validate the eligible area of open space your community is claiming per parcel. If only a small portion of the parcel overlaps the floodplain area, only that overlapping area is eligible, not the entire parcel. To make your final analysis easier, you'll remove the smallest parcels.
- On the attribute table's ribbon, click Select By Attributes.
- In the Select By Attributes window, confirm that Input Rows is set to Parcels_Zonal and Selection Type is set to New selection.
- Use the drop-down menus to create the query ACRES is less than 1.
- Click OK.
The acreages that meet your query are now highlighted in the attribute table. These are the pieces of land that are likely too small to provide many credits.
- On the attribute table's ribbon, click Delete.
There are 245 parcels remaining. Next, you'll save your edits.
- On the ribbon, click the Edit tab. In the Manage Edits group, click Save.
- In the Save Edits window, click Yes.
- Close the Parcels_Zonal table.
Join the datasets
You now have all the information you need, but it is spread across three locations: your parcel dataset, the zonal table, and the PADUS_CRS_attrib table. The CRS review process requires that you report eligible OSP acreages per parcel. You ultimately need the OSP acreage values and the PADUS information included in the attribute table of your parcel dataset. To accomplish this, you will use multiple joins to integrate this data by a common attribute.
- In the Contents pane, right-click the GeorgetownCo_Parcels layer, point to Joins and Relates, and choose Add Join.
The Add Join window appears.
- For Input Join Field, choose PARCEL_ID.
- For Join Table, choose Parcels_Zonal. For Join Table Field, choose PARCEL_ID.
Note:
You may receive a warning about the join field not being indexed. Indexes are useful if you need to query your data frequently, as they speed up searches in ArcGIS. For the purpose of this analysis, your data will be used for presentation purposes, not continued use, so you won't index it.
- Click OK.
- Open the GeorgetownCo_Parcels attribute table and confirm that the Parcels_Zonal attributes (ZONE_CODE, COUNT, and so on) have been added.Most of the records will have null values for the joined fields, because you created the Parcels_Zonal table by removing smaller parcels from the GeorgetownCo_Parcels layer. You want to keep all of the records, despite the null values, because you have another dataset to join to the GeorgetownCo_Parcels layer.
- In the Contents pane, right-click the GeorgetownCo_Parcels layer again. Point to Joins and Relates, and choose Add Join.
- In the Add Join window, for Input Join Field, choose MAJORITY.
- For Join Table, choose PADUS_CRS_attrib. For Join Table Field, choose OBJECTID.
- Click OK.
- In the GeorgetownCo_Parcels attribute table, confirm that the PADUS_CRS_attrib fields (Category, Own_Type, and so on) were added.
For the CRS review process, you only need to submit the parcels you claim are OSP eligible. Next, you'll filter these out.
- On the attribute table's ribbon, click Select By Attributes.
- In the Select By Attributes window, confirm that Input Rows is set to GeorgetownCo_Parcels and Selection Type is set to New selection.
- Create the expression MAJORITY is not null.
- Click OK.
The result is a comprehensive dataset of parcels with at least 1 acre of likely eligible open space and all the attributes from the PADUS dataset.
- Below the attribute table, click the Show selected records button.
Only those records that match your criteria are shown.
Note:
Your number of selected records may be different than the number shown in the image above. This is due to updates to the Open Space Preservation Community Rating dataset. If your number is different, your final map will also vary from the one shown in this tutorial.
Next, you'll export these results so you can symbolize them.
- In the Contents pane, right-click GeorgetownCo_Parcels, point to Data, and choose Export Features.
- For Output Feature Class, type GeorgetownCo_OSP. Click OK.
When the tool finishes, the new GeorgetownCo_OSP layer is added to the Contents pane.
- Close the attribute table and save the project.
You've learned how to aggregate raster information into parcel zones and used a network of joins to create a comprehensive parcel data table that contains all the information required for the CRS review process. Next, you'll create a custom map to pair with the final parcel data table that your planner can submit to apply for CRS credits during the review process.
Create a print map
Previously, you used zonal statistics and joins to create a comprehensive parcel dataset. Next, you'll address the final requirement of the CRS review process by creating a custom print map that visualizes this information and a supporting parcel table.
Create a layout
To complete the review process, the Insurance Services Officer needs the spatial information you found to verify OSP eligibility and determine the number of credits your community will receive. Until now, you've been working in the map view. To create a custom exportable map, you'll add a layout view.
- If necessary, open your CRS_Georgetown_Co project.
You'll change the basemap to one that is more neutral and distracts less from the thematic data.
- On the ribbon, click the Map tab. In the Layer group, click Basemap. Choose the Light Gray Canvas basemap.
- On the ribbon, click the Insert tab. In the Project group, click New Layout.
- In the drop-down menu, under the ANSI - Portrait group, choose Letter.
A new layout appears.
- On the ribbon, on the Insert tab, in the Map Frames group, click the Map Frame button. In the drop-down menu, choose the second map.
- Draw a rectangle on the layout to place the map frame.
Next, you'll fix the positioning of the map frame.
- Double-click the map frame to select it.
The Element pane appears.
- In the Element pane, click the Placement tab.
- In the position diagram, ensure that the lower left corner is selected. Set the following properties:
- For Width, type 7.7 in.
- For Height, type 9.5 in.
- For X, type 0.4 in.
- For Y, type 0.4 in.
The map frame is now neatly positioned on the layout, with an even margin on the sides and bottom, and a larger margin on the top.
- If necessary, in the Contents pane, expand the Map Frame and Map items until you can see all the layers.
- Uncheck the following layers and ensure all other layers are turned on:
- GeorgetownCo_Parcels
- PADUS_CRS_final.tif
- Open Space Preservation Community Rating System
- Right-click Community_Boundary and click Zoom To Layer.
The map is now neatly positioned within the map frame.
Next, you'll change the symbology of the GeorgetownCo_OSP layer to improve its visibility on the map.
- In the Contents pane, right-click GeorgetownCo_OSP and choose Symbology.
The Symbology pane appears.
- In the upper right corner, click the options button and choose Import symbology.
The Geoprocessing pane appears, open to the Apply Symbology From Layer tool.
- For Symbology Layer, click the Browse button and choose OSP_Eligible_Parcels.lyr from the project folder.
- Click Run.
The saved symbology is applied to the GeorgetownCo_OSP layer. The map still needs a few elements to help viewers, such as a scale bar and legend.
- On the ribbon, on the Insert tab, in the Map Surrounds group, click North Arrow.
- In the lower right corner of the map, on the water, draw a rectangle to add the north arrow. Resize it if necessary.
The default north arrow is added to the map.
- In the Map Surrounds group, click the lower half of the Legend button. Click Legend 2.
- In the upper left corner of the map, draw a rectangle to add the legend.
Add and format text
To finish the map, you'll add a title and edit the text of the legend to make it more legible.
- On the ribbon, on the Insert tab, in the Graphics and Text group, click Rectangle Text.
- Draw a rectangle above the map to insert a text box. Make it the same width as the map.
- Type Georgetown County, SC. Press Enter and type Impact Adjustment Map for Open Space Preservation Activity 420 — Element 422a.
- Click outside of the text box to finish typing. Click the text box to select it.
- On the ribbon, click the Text tab. In the Text Symbol group, change the size to 14 pt and the alignment to Center.
- Highlight the first line of text. In the Text Symbol group, change the size to 16 pt and the style to Bold.
Next, you'll change the names of some of the map's layers to make the legend easier to understand.
- In the Contents pane, edit the name of the GeorgetownCo_OSP layer to OSP Eligible Parcels.
- Edit the name of the Community_Boundary layer to Community Boundary (replace the underscore with a space).
- Under 100-year Floodplain, click ZONE_COMBI and press F2. Delete the text.
The heading disappears from the legend.
You'll make one more change to the legend, to reduce the size of the 100-year Floodplain text.
- On the layout, click the legend to select it.
- In the Element pane, click the Text Symbol tab.
- Expand the Appearance group. For Size, choose 12 pt.
- Click Apply.
The layout is complete.
Next, you'll export the layout.
- On the ribbon, click the Share tab. In the Output group, click Export Layout.
- In the Export Layout window, for File Type, choose PNG. For Name, click the Browse button.
- In the Export Layout window, choose a location. For Name, type Georgetown CRS. Click Save.
- For Resolution, type 300.
- Click Export.
Your planner can use this map in the county's application for CRS credits along with the parcel table you'll create next.
Note:
Although the FEMA CRS application process requires planners to submit finished maps and tables that can be printed, you can also export your final product as a web map service to your organization's ArcGIS Online account or an enterprise server: Open the map view. On the ribbon, click the Share tab. In the Share As group, choose Web Map or Web Layer.
- Close the Export Layout, Element, and Symbology panes.
Export and edit the parcel table
The CRS application process requires both spatial and tabular information for OSP eligibility per parcel. You'll export your parcel dataset attribute table to a .csv file to prepare and format the information in a clear and concise way for the CRS reviewer.
- In the Contents pane, right-click OSP Eligible Parcels, point to Data, and choose Export Table.
The Export Table window appears.
- In the Export Table window, confirm that Input Table is set to OSP Eligible Parcels. For Output Table, type Georgetown_OSP_Table.
- Click OK.
The table is added to the Contents pane under Standalone Tables.
- Reopen the Geoprocessing pane. Search for and open the Table To Excel tool.
- For Input Table, choose Georgetown_OSP_Table.
- For Output Excel File, type Georgetown_OSP_Table.xls. Check the Use field alias as column header check box.
- Click Run. Save the project.
- In your computer's file explorer, browse to where you saved the Excel table and open the Georgetown_OSP_Table.xls file with Excel.
Note:
If you don't have Excel, open the file with Notepad or a similar text editor.
- Delete the following fields:
- STATE_CODE
- CNTY_CODE
- GIS_acres
- OBJECTID
- PARCEL_ID
- AREA
- MAJORITY
- OBJECTID_1
- OBJECTID
- Own_Name
- Mang_Name
- State_Nm
- SHAPE_length
- SHAPE_Area
- Shape_Length
- Shape_Area
- Change the field names based on the following table:
From To ACRES
OSP Eligible Acres
CATEGORY
OSP Type
Own_Type
Owner Type
Loc_Own
Local Owner
Mang_Type
Local Manager Type
Loc_Mang
Local Manager
Loc_Ds
OSP Description
Loc_Nm
Local Name
GIS_Acres
Total Parcel Acres
- Save the spreadsheet.
In this tutorial, you used a national-scale raster image service to perform a parcel-scale analysis that can help your community save money on flood insurance while reducing their flood risk. Your planner will use the map and parcel data table you created to submit for OSP points in the upcoming CRS review. Assuming all OSP areas you've identified are validated, your hope is that Georgetown County can move from CRS Class 8 to Class 7. That move would equates to a 15 percent discount on flood insurance for policyholders within the 100-year floodplain, and 5 percent for those outside the floodplain. These savings would amount to more than $1 million in total annual savings across the community, or $128 per policyholder. Your planner can also use the data you generated to help influence land-use management planning, prioritize future open space in the floodplain, make the case for policy or regulatory changes such as raising base flood elevations or rezoning, and to more effectively engage decision makers and landowners about flood risks and nature-based solutions such as preserving open space.
You can find more tutorials in the tutorial gallery.