Symbolizing the NHD in ArcMap
This exercise is done in ArcGIS 9.3.1
Background: The NHD is a complex set of data containing information on surface water. In addition to providing points, lines, and areas for mapping, the NHD also contains coded values that enable users to perform hydrologic modeling. The NHD reach addressing system allows for modeling upstream and downstream relationships. Measures pinpoint an exact location on a reach. This addressing system, in combination with the NHD flow network, allow for modeling using the NHD.
Goal: In this tutorial you will learn how to symbolize by feature type (Ftype) and how to symbolize by feature code (FCode).
Step 1 Setup ArcMap Session
Copy the .mdb found here. In Windows explorer, unzip the file. The Subbasin used in this tutorial is 17050108, The Jordan Subbasin.
Want to know more about the WBD?
Create a new document (.mxd)
Click the add data button and navigate to the .mbd. An .mdb is a personal geodatabase. In the window click on the geodatabase. Select the first item (hydrography) and hold the Shift button while you click the last item on the list. Click the "Add" button. All items in the menu should be highlighted.
All the datasets and tables will appear in the table of contents (TOC). In the map, the data will appear to be very small. This is because the map is zoomed out to a small scale view of the United States. Note: You will get a warning that one item cannot be added. Click OK.
Zoom to the data in ArcMap by using the magnifying glass and drawing a box around the data.
The first thing you will see is a point layer. These points are the network or Hydro_NET_Junctions. Each flowline has a point on it's from and to nodes. The NHD network is what allows for upstream and downstream tracing on NHD Flowlines.
Turn Hydro_Net_Junction off by clicking the box next to its name in the table of contents.
Double click on the Data Frame. This should be called "Layers".
Click the Coordinate System tab. You will see the Current Coordinate System is GCS_North_American_1983. The NHD is unprojected when you download it. It comes in a Geographic Coordinate System (GCS) of the North American Datum (Also referred to NAD) of 1983.
Click OK to close.
Step 2 Symbolize Data by FType
Each feature class in the NHD is broken down into Feature Types, or FTypes which have a coded value in addition to a name. For example, the feature type StreamRiver is coded as Ftype 460.
Double-Click on NHDFlowline in the TOC or right click and choose the option for Properties.
Click on the Symbology tab.
Make sure the Value Field is set to FType.
Adjust the symbology of the flowline features so it looks like this:
To do this, double click on the line symbol and choose the line that has an arrow on the end. Follow the steps in the following graphic:
In the Symbol Property Editor follow the directions in the following graphics to change the color of the arrow head.
Once all your flowlines are symbolized with the appropriate color, the map will display the Hydrography Data with symbology that looks like this:
If you will be using this symbology frequently, you can save it as a layer file to save time in the future.
Step 3 Symbolize Data by Fcode
Many FTypes are attributed by FCodes, which provide descriptive information about the feature. For example the FType StreamRiver Code 460 may be broken into FCode 46000 which refers to a perennial stream, or 46002, an ephemeral stream. Some FTypes are broken into more than 10 different FCodes. This allows for features to be specifically attributed according to their real-life characteristics. Using a code to do this allows for users to easily query or display specific feature descriptions.
Open the NHDFlowline properties menu and click on the Symbology tab.
In the Value Field change the drop down menu to Fcode.
Click "Add All Values".
The Fcode appears on the left side of the window under "Value" while its description appears on the right side of the window under "Label".
Expand the Label field to see a complete explanation of the attributes.
The Fcode provides information on the feature type, the purpose of the feature and sometimes the relationship to the surface or stage level of the water.
Remove all the features leaving only StreamRiver features. You can do this by selecting the features, then click the "Remove" button.
Uncheck the box next to "all other values".
Your Symbology window should look like this:
There are four values for StreamRiver. No attributes, 46000, Ephemeral, 46007, Intermittent, 46003, and Perennial 46006.
Symbolize 46000 and 46006 with a blue arrowed line. Symbolize 46007 as a brown arrowed line.
Symbolize 46003 with a dashed, blue, arrowed line.
Your symbols should look like this.
Quiz: Use the skills you learned in this tutorial to answer this question.