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I have a number of point features which contain an attribute I call "bearing" and another one called "slope". Each point has a bearing between 0 to 359 degrees. And the slope is either "+15" or "-15", etc, such as +15% or -15% depending on the steepest slope of the ground.

What I am wanting to do is display an arrow on the map with the arrow pointing in the bearing direction. With a negative slope% pointing outward from the point and a positive slope% pointing inward to the point.

I'm using this in a forestry context with cruise plots. I'm fairly certain that ArcGIS can do this (As I've seen it on maps) but I'm hoping that QGIS can as well.

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up vote 5 down vote accepted

You can also try this: open the layer properties and click Change.. under the displayed symbol. Then pick Vector Field Marker as the layer type in the top right and Polar as the field type. Fill in the appropriate fields and you should get what you want, though the lines' length will be scaled by slope (use a small scale to get rid of that if you want). Add another symbol or change the LineStyle to get arrow tips on the ends of the line. I didn't have any appropriate data handy, so I'm not sure if the tips get oriented properly though.

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Ah yes, I'd forgotten about "Polar", but definitely go with this. I still think it would be necessary to load the shapefile in two layers though. Nick. –  nhopton Jun 27 '12 at 14:55
    
Thanks so much you two for your help. It worked great and it looks good on a map. I did need to make 2 point shapefiles so that the arrows would point their respective ways into and out of the plot center. I appreciate it alot. –  Jeremy Jun 28 '12 at 3:52
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This should be possible. The simplest way is probably to load the shapefile with the points, right-click on it in the layers panel, select "Query" and select the points with the negative slopes. Then load the shape file again and query to select the points with the positive slopes. You will then be able to style the two layers differently (it will help to avoid confusion if you rename the layers, as shown in the picture).

When you are applying rotation to the symbols remember that so far as the new symbology is concerned the horizontal is 0-degrees, so you'll need a new column in the attribute table for rotation (the compass bearing minus 90).

In the picture I've also added the shapefile (again!) so that the original points are visible. Hope this works, it's not been stress tested.

Regards, Nick.

enter image description here

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