This is a QGIS vs. ArcGIS throwdown. It has been a while since I did the last one on
kernel density
and Thiessen polygons. Recently, I was looking over new QGIS plugins and one in particular caught my eye: the
QGIS Magnetic Declination Plugin
.
Magnetic declination
is simply the difference between geographic and
magnetic north
, caused by the earth's magnetic fields.This difference also changes over time. ESRI has a nice
technical article on their blog
.
|
NOAA Historical Magnetic Declination Viewer: http://maps.ngdc.noaa.gov/viewers/historical_declination/ |
Adding a declination diagram in ArcGIS can be a bit tricky. As of version 10.2, there is a template and several tools to assist. You will need a Standard or Advanced license plus the Production Mapping Extension.
QGIS Plugin
You can select a location off a map, such as OpenStreetMap, calculate it and map it! Best of all, the resulting compass rose and measurements also appear in QGIS Print Composer. Under the options tab, you can also change the color. I found it helpful to change it to black.
Steps:
- Click LON/LAT from map
- Choose any options
- Press "Calculate" button
- Then "Draw Compass Rose"
|
Screenshot of the plugin, steps, and buttons. |
- Click any of the screenshots below to get a closer look.
|
Up close example with declination, true, and magnetic north shown in Greenland where declination is much greater. |
 |
Showing positive, zero, and negative declination in the US. |
Update #1
I forgot to mention that you can customize the size/diameter of the compass rose--as large or as small as you need depending on whether you are interested adding it to a small scale map or a large scale map.
أكثر...