Navigating the Network: Part 1
Explore NHD features that enable the flow network
Step 1 Open the .mxd
In this tutorial, we will be working with The Blue River Subbasin, HUC 14010002. Copy this zip file onto your computer's local directory.
Unzip the file.
Within the zip file, there is a geodatabase that holds all the data for the tutorial called “BlueRiver.mdb”. There is also an mxd that has all the data properly symbolized and is called “Navigating the NHD Flow Network.
First, Open the mxd and set the data connections of the layers to point to their features within the BlueRiver geodatabase.
Step 2 Explore NHD Feature Classes.
Turn on the layer called Hydro_Net_Junctions.
Right click the layer and select "Zoom to Layer".
You will see a point layer.
Zoom in to a larger scale, around 1:160,000
Turn on the Flowline Group Layer.
You can now see that there is a Hydro_Net point at the from and to nodes of each flowline.
The Symbology of the flowlines is set to have a scale dependency. Once you zoom in to a scale of 150,000 or larger, the flowlines will be symbolized by Ftype and also have flow direction. The blue arrows at the end of each flowline represents it's flow direction.
Zoom in to 1:150,000 or larger.
Select a flowline and open the attribute table.
Tip: Set selectable layers only to NHDFlowline
Choose the option to only show selected features.
Drag the scroll bar on the bottom of the attribute table until you see the field called "FlowDir" This feature is attributed as "With Digitized" meaning that it's flow direction is known and it participates in the flow network. If flow direction is unknown, this field will be populated as "Uninitialized "
Can you think of an application that relies on NHD flow direction?
Turn off the Hydro_NET_Junctions layer.
Navigating the Network: Part 2