This can be done by altering the Properties of the Data Frame. Doing so will cause ArcMap to have to re-project the data 'on-the-fly' from the original coordinate system of the data to the new coordinate system of the Data Frame. When using this coordinate system, note how the lines of latitude and longitude create square boxes.
In reality, the lines of longitude should be converging towards the north pole. This is an example of a type of map distortion that is introduced by the coordinate system To learn more about projection on the fly, read this blog article. The new projected coordinate system is applied to your map. The analysis results are now presented in a form that preserves relative areas, so your map readers can accurately compare the sizes of precipitation anomalies.
Below is a comparison of the two projections at the same scale. How might the Web Mercator projection mislead or hinder people from properly interpreting your analysis results?
The Equal Earth projection is designed to show the entire world, but there are two parts of the world that it is unable to map effectively. Next, you'll try a projection designed to map polar regions. A compass needle does not point to the true north pole. Instead, it points to the magnetic north pole , a location that is constantly changing. Next, you'll make a map to show the wandering path the magnetic pole has taken over the past years.
You also want to use this map to show whether the magnetic north pole is moving closer to, or farther away from, true north. You'll search for a projected coordinate system that preserves distances from the north pole.
The map does a poor job of illustrating the changing location of the magnetic north pole. The points all appear to be far away from the true north pole, and they are also split up on either side of the map. Measurements made on this map would be meaningless. Next, you'll find an appropriate projected coordinate system by searching for keywords. This map currently uses a geographic coordinate system, WGS You can read more about the difference between geographic and projected coordinate systems in this blog article.
Drag the edges of the Map Properties window to make it larger. There are only two projected coordinate systems, one for the north pole and one for the south pole. This projection distorts both angles and areas. Distortion is extreme in the southern hemisphere. However, this projection is useful for mapping the area around the north pole. It preserves true distances and directions measured from the pole.
There are some problems with the Topographic basemap. This basemap was designed for the Web Mercator projection, so it becomes squished and stretched when it is reprojected onto the Azimuthal Equidistant map.
The Topographic basemap is not suitable for your polar map, so you'll find one that is. Next, you'll use your map to measure distances between true north and the wandering magnetic north pole, to determine the year when they were closest. Snapping will allow you to measure features more easily. The Measure Distance window appears on top of the map. The tool reports a distance of Magnetic north was nearest to true north in , when it was It is now heading south, toward Russia.
You can make true distance measurements on this map because it uses an equidistant projection. However, no projection can preserve all distances. The azimuthal equidistant projection preserves distance and direction from the central point only. So measurements from the north pole are true, but measurements between any other locations on this map will be inaccurate.
The measurements you've made so far have been planar. Planar distances are like measuring with a ruler on a paper map. Geodesic distances are like measuring with a string over the surface of a globe.
Next, you'll compare planar and geodesic measurements between the magnetic north poles of and The distance reported between these two locations is 1, However, the only accurate planar distances that can be made on this map are from the center point. To find accurate distances between other locations, you need to make geodesic measurements. This time, the reported distance is 1, The geodesic distance is over kilometers longer than the planar distance.
Geodesic distances ignore the map's projection and provide a true distance. Planar distances are only true if the map uses a distance-preserving projection, and only to certain points or along certain lines. The projected coordinate system you chose for this map was already centered on the north pole, which happened to be the location from which you wanted to measure. But what if you wanted to measure from a different point? Next, you'll modify the existing coordinate system to center it on the magnetic north pole, so measurements can instead be made from that point.
The Longitude and Latitude are listed in the pop-up. The coordinates of the pointer can also be read in the toolbar beneath the map.
The Modify Projected Coordinate System window appears. Here, you can construct a custom coordinate system with parameters that match your needs. The Projection is already set to Azimuthal Equidistant. A projection and a projected coordinate system are not the same thing. A projection is one parameter in a projected coordinate system. Other parameters include a geographic coordinate system, a linear unit, and a set of parameters that depend on the selected projection central meridian, scale factor, and so on.
Learn more about coordinate systems in the blog article Coordinate Systems: What's the Difference? You'll adjust the parameters for this projected coordinate system to center it on the chosen location, instead of true north. It is also listed in the Custom category of available coordinate systems. Coordinate systems in the Custom category are not saved. Next, you'll add it to a favorites folder so you can use it in future maps. Favorite coordinate systems are stored as.
The map redraws with the new projected coordinate system. It looks similar to before, but the center of the map if not the basemap has shifted. Both geodesic and planar measurements from the new point will now be accurate. In ArcGIS, you can choose between planar or geodesic measurements. But your map reader will not have this choice; they will only see a flat map on a screen or piece of paper.
An equidistant projection is the right choice for this map to allow everyone to assess distance correctly from the north pole. Because of this, the GCS really just provides the datum. Since the datum just includes the ellipsoid, or shape of the earth, we can consider a GCS to just include an ellipsoid..
You can see the contents of a GCS by opening a ". Use the ". Projected coordinate systems use rectangular or Cartesian Coordinates. You learned about rectangular coordinate systems in geometry and used X and Y as the values.
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