What type of map projection would you use if you wanted to preserve shapes?
Projections are calculations that allow you to draw the round earth on a flat screen or piece of paper. If you've made a map before, you've used a projection. Show
Every map deforms the earth. It is impossible to represent a curved surface (the earth) on a flat one (a map) without stretching, skewing, and tearing it. Map projections apply this distortion in a systematic way that allows you to control where and how it happens. This lesson will introduce you to tools and techniques to help you choose the right projection for your map. This lesson was last tested on May 23, 2022, using ArcGIS Pro 3.0. If you're using a different version of ArcGIS Pro, you may encounter different functionality and results. Lesson PlanUnderstand projectionsYou will not find a projection that is suitable for all maps. All projections distort the earth in some way. Each one seeks to preserve some geometric property at the expense of others. Projection typesConformal projections preserve angles locally, so the shapes of features appear true. But the cost of this quality is the distortion of areas and distances. Equal area projections preserve area, at the expense of angles, so the shapes of some places appear skewed. Equidistant projections preserve distances, although only from certain points or along certain lines on the map. Three maps, drawn with examples of conformal, equal area, and equidistant projections, overlaid with geodesic circles that demonstrate geometric distortions.Compromise projections provide a representation of the earth that is not perfectly correct in any way but not badly distorted in any way either. They are usually used for maps of the entire world. There are dozens of projections available in ArcGIS that can be configured into countless projected coordinate systems. Your choice of a projected coordinate system depends on many factors, including the part of the world you are mapping, the scale of your map, and the purpose of your map. You want to choose a projected coordinate system in which the places and properties that are most important to your map are the least distorted. Map global analysis resultsMap projections distort the grid of latitude and longitude lines, which means they also distort your data. You've taken great care to conduct an analysis of future precipitation changes properly and precisely. Next, you need to present your results on a map. You want to choose a projection that will allow you to present those results clearly, so they are not misinterpreted. Find a global equal area projectionFirst, you'll explore a few traditional resources to help you find a suitable projection for your analysis results.
Change the map's projected coordinate systemYou've decided to use the Equal Earth projection. Next, you'll apply it to your Precipitation Change map.
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. Map polar dataA 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 400 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. Find a polar equidistant projectionYou'll search for a projected coordinate system that preserves distances from the north pole.
Find the northernmost magnetic poleNext, 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.
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. Measure geodesic and planar distancesThe 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 1590 and 2020.
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? Modify a projected coordinate systemNext, you'll modify the existing coordinate system to center it on the 1590 magnetic north pole, so measurements can instead be made from that point.
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. Sometimes, you won't find a projected coordinate system that is ready-made for your map's purpose. ArcGIS Pro allows you to modify any coordinate system to have parameters that better suit your needs. Next, you'll learn how to create a custom projected coordinate system using suggested parameters from ArcGIS Pro. Map the border of two UTM zonesUniversal Transverse Mercator (UTM) is a system that is commonly used for large-scale maps. If your map is narrower than 6° of longitude, you can map it with a UTM projected coordinate system. The map you'll make next is narrow enough but doesn't fit properly into an existing UTM zone. In this lesson module, you'll learn how to find the correct UTM projected coordinate system for an area of interest, and how to create a custom projected coordinate system to use when a standard UTM zone doesn't fit. Find the correct UTM zoneYou want to map the border between Finland and Russia. This will be a reference map, meant to give descriptive context to the border region. You want to use a conformal projection to show the shapes of features in their most recognizable forms.
The World_UTM_Grid layer confirmed that the best choice for this map is a custom projected coordinate system. Next, you'll create one for this region. Create a custom projected coordinate systemArcGIS Pro can suggest new custom projected coordinate systems based on two criteria: distortion property and map extent.
Earlier in this lesson, you learned how to modify coordinate systems. How could you modify an existing UTM coordinate system to center it on the Russia-Finland border? How could you modify the Equal Earth projection from the start of this lesson to better show the Pacific Ocean? Tip:Copy and modify any WGS 1984 UTM Zone coordinate system. Change the central meridian to 29.9. Copy and modify the Equal Earth (world) coordinate system. Change the central meridian to 160°W or a similar value. In this lesson, you learned some techniques and explored resources that will help you choose an appropriate map projection:
Take a closer look at the maps you see on the internet, in the news, or in apps. Do they use a projection that is well suited to their purpose? Are their distance and area measurements accurate? The consequences of ignoring your choice of map projection include distorting your data and misleading your map readers. However, if you spend some time to find an appropriate projected coordinate system, you'll create a map that presents your data and your message clearly and accurately. You can find more cartography lessons on the How to make a map page. Acknowledgements
Send Us FeedbackPlease send us your feedback regarding this lesson. Tell us what you liked as well as what you didn't. If something in the lesson didn't work, let us know what it was and where in the lesson you encountered it (the section name and step number). Use this form to send us feedback. What type of map projection preserves the shapes?Conformal projections preserve local shape. To preserve individual angles describing the spatial relationships, a Conformal projection must show the perpendicular graticule lines intersecting at 90-degree angles on the map.
What type of map projection would you use if you wanted to preserve shapes rather than area?Every map projection distorts one or more of the four basic spatial properties: shape, area, distance, and direction. The Mercator projection is a cylindrical projection invented by Gerardus Mercator. It preserves the spatial property of shape.
Which map projection type preserves the property of true shape?'equal-area' projections preserve true areas. 'conformal' projections preserve true shape. 'azimuthal' projections preserve true compass direction from the centre.
What type of projection is best used to preserve distance?Equidistant projections preserve distances, although only from certain points or along certain lines on the map. Three maps, drawn with examples of conformal, equal area, and equidistant projections, overlaid with geodesic circles that demonstrate geometric distortions.
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