Displaying Flow Direction as Arrows using a Flow Direction Raster Layer

[Moore, Rick (MNIT)]

Happy Friday All – I am just throwing this out here as a tool that I have found useful in the process of hydro-modification.  As I place breachlines and rerun the Manual Cutter tool, I like to see how the flow direction is affected by the breachlines I place.  The use of Vector Field under Symbology allows me to do this and the drawing of the arrows is very quick.  I used to do this from making points from the cells and then assigning arrows to the different directions.  This process is faster and takes up a lot less space.

Thanks,

Rick Moore

LiDAR Data Steward-GIS Analyst | Ecological and Water Resources

Minnesota IT Services | Partnering with Department of Natural Resources

117 Rogers Street

Mankato, MN, 56001

Desk: 507-389-8810

Office: 507-389-8800 | rick....@state.mn.us  | Lat 44.16322 Long -94.03001

Information Technology for Minnesota Government | mn.gov/mnit

Displaying Flow Direction as Arrows using a Flow Direction Raster Layer

1.       Use the Flow Direction output from the Manual Cutter Tool or the Flow Direction Tool.

2.       Reclassify the Flow Direction Raster using the following values:

a.       1 = 90

b.      2 = 135

c.       4 = 180

d.      8 = 225

e.      16 = 270

f.        32 = 315

g.       64 = 0

h.      128 = 45

3.       The Flow Direction values that come from the Flow Direction Raster are converted to Angles.

4.       Open the Layer Properties for the new reclassified layer – Flow Direction Angle and click on Symbology

5.       Click on Vector Field under Show: on the left side.   Use the following values:

a.       Input represents U and V components: Unchecked

b.      Magnitude Component: None

c.       Direction Component: Flow_Direction_Angle – Band_ 1

d.      Symbology Settings - Symbol: Single Arrow

e.      Each symbol represents a tile of size: 1 (Screen Pixels)

f.        Thinning Method: Vector Average (Since tile size is 1 this will not be implemented)

g.       Leave other values as their default.

6.       Set the Scale Range under General so that the layer does not draw past a set scale

a.       Click Don’t Show Layer When Zoomed:

                                                               i.      Out Beyond: 1:750 (minimum scale)

7.       For each new iteration of the Manual Cutter Tool or the Flow Direction Tool, the process will need to be repeated so that the arrows are reflective of the most recent flow direction raster.

8.        Values used for the Vector Field.

9.       Close up of Flow Direction Arrows.