Choose the right projection (2023)

You will not find a suitable projection for all maps. All projections distort the earth in some way. Each tries to preserve some geometric properties over others.

types of projection

Conformal projections preserve angles locally, making feature shapes look real. But the price of this quality is the distortion of areas and distances. Equal-area projections preserve area at the expense of angles, causing shapes to appear distorted in places. Equidistant projections maintain distances, but only from specific points or along specific lines on the map.

Choose the right projection (1)

Compromise projections provide a representation of the Earth that is by no means perfectly accurate, but it is also not grossly distorted. They are usually used for maps of the whole world.

There are dozens of projections available in ArcGIS that can be set to any number of projected coordinate systems. Choosing 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 where the key locations and features for your map are less distorted.

Map projections distort the grid of latitude and longitude lines, which means they distort your data as well. They have taken great care to conduct a proper and accurate analysis of future changes in precipitation. Next you need to present your findings on a card. You want to choose a projection that allows you to present these results clearly so they are not misinterpreted.

Find a global equivalent area projection

First, you'll explore some traditional resources to help you find an appropriate extrapolation for your analysis results.

  1. Download theProjection Project package.
  2. Locate the downloaded oneProjections.ppkxfile on your computer. Double-click the file to open itArcGIS Pro. If prompted, log in to yourArcGIS onlineÖArcGIS EnterpriseAccount.
    Use:

    If you haven'tArcGIS Proor have an ArcGIS account, you can sign up for oneFree ArcGIS Trial.

    The project has three cards. Hechange precipitationThe card is active.

    Choose the right projection (2)

    Show the data on this mapPrecipitation anomalies forecast for the years 2040 to 2059More precipitation is forecast for green areas in the future compared to historical averages. Brown areas are expected to be less experienced.

    First, it is determined which projection this map uses.

  3. NOSatisfiedControl panel, right-clickchange precipitationand chooseCharacteristics.

    Choose the right projection (3)

  4. NOcard propertieswindow, clickcoordinate systemEyelash.

    LowXY really, you can see that is the current coordinate system for this mapWGS 1984 Web Mercator (auxiliary bullet).

    Choose the right projection (4)

    Web Mercator is a general purpose coordinate system developed for web mapping applications. Most of Esri's basemaps are tiled in Web Mercator, so they may be more compatible. However, this projection does not preserve areas, distances, or angles.

  5. NOcard propertiesclick on the windowCancel.

    When you look at this map, you might think that Greenland is many times larger than India. In fact, Greenland is slightly smaller than India. When the Web Mercator projection skews the relative sizes of countries so dramatically, you know it must also skew the results of your analysis.

    This map suggests that the areas that will experience the most extreme changes in precipitation are a relatively small part of the Earth, just a narrow band along the equator. Web Mercator is not a viable option for this map. You'll then see a chart that compares the projections to find one that fits your map.

  6. OpenQuick notes on map projections in ArcGIS.

    Choose the right projection (5)

    The most important property to maintain on your precipitation map is area. This applies to most maps that display analysis results using area, density, or distance comparisons.

  7. Use the table to find a projection that meets the following criteria:
    • Properties: same area
    • Matching extension: world
    • General Purpose: Thematic

    There are some projections that are suitable for your map. One of them is Equal Earth.

    Choose the right projection (6)

  8. go toArcGIS Prohelp page forland soonProjection. Scroll down and read theUseSection.

    You can learn about all of the projections found in ArcGIS to decide which one is best for your map.

Change the map's projected coordinate system

You have chosen the Equal Earth projection. You then apply it to your precipitation change map.

  1. EmArcGIS Pro, NOSatisfiedControl panel, double clickchange precipitationto open thecard propertiesVentana.
  2. click nocoordinate systemEyelash.
  3. Type in the search barland soonand pressureEnter.

    The list of available coordinate system filters is based on your search.

  4. ExpandProjected coordinate systemand expandWelt. give clicksame earth (world).

    IsXY reallyThe button updates to show that the map's coordinate system has changed.

    Choose the right projection (7)

    Advice:

    Change the coordinate system tocard propertiesWindow only affects the map. The coordinate system of your data layers is not changed. Planes are projected in real-time to be drawn correctly on the map. To learn more about motion projection, read thisblog article.

  5. NOcard propertiesclick on the windowACCORDINGLY.

    The redesigned coordinate system is applied to your map.

    Choose the right projection (8)

    Analysis results are now presented in a way that preserves relative areas, allowing your map readers to accurately compare the size of precipitation anomalies.

  6. About itQuick access to the toolbar, CliqueSave on computerto save the project.

    Choose the right projection (9)

Below is a comparison of the two projections at the same scale. How can the Web Mercator projection mislead or make it difficult to correctly interpret the results of your analysis?

Choose the right projection (10)

The Equal Earth projection is designed to show the entire world, but there are two parts of the world that it cannot depict efficiently. Next, you'll test a projection for mapping polar regions.

A compass needle does not point to the true north pole. Instead, it points to themagnetic north pole, a place in constant change. They will then create a map to show the errant 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 toward or away from true north.

Finding a polar equidistant projection

You're looking for a projected coordinate system that maintains distances from the North Pole.

  1. Click the button at the top of the map viewNorth PoleTab to activate this map.

    Choose the right projection (11)

    The data for this map was provided byNOAA National Environmental Information Centers (NCEI).

    The map shows the changing position of the magnetic north pole poorly. All points appear to be far from the true North Pole and are also shared on either side of the map. Measurements on this map would make no sense.

    You have two criteria for the projection of this map:

    • In order to display the Arctic data as naturally as possible, you need a projected projection for the polar regions.
    • To determine how close magnetic north is to true north, you need an equidistant projection that maintains accurate measurements of the distance to the north pole.

    Find a suitable projected coordinate system below by searching for keywords.

  2. NOSatisfiedControl panel, double clickNorth Poleto open thecard propertiesVentana.
    Use:

    This map currently uses a geographic coordinate system, WGS 1984. When a geographic coordinate system is selected, your map is projected using the Pseudo Plate Carrée projection. You can read more about the difference between geographic and projected coordinate systems hereblog article.

  3. About itcoordinate systemleadership, researchEquidistant.
  4. expand thatProjected coordinate systemenumerate and expandPolar.

    Choose the right projection (12)

    Advice:

    Drag the edges ofcard propertieswindow to make it bigger.

    There are only two projected coordinate systems, one for the North Pole and one for the South Pole.

  5. give clickNorth Pole Azimuthal Equidistantand clickACCORDINGLY.

    This projection distorts both angles and surfaces. Distortion is extreme in the southern hemisphere.

    Choose the right projection (13)

    However, this projection is useful for mapping the area around the North Pole. It maintains the actual distances and directions measured by the pole.

  6. NOSatisfiedControl panel, right-clickHistoricMagneticPoloTrackand choosezoom to level.

    Choose the right projection (14)

    There are some issues with the topographic basemap. This basemap was designed for the Web Mercator projection, so it will always stretch when projected onto the Azimuthal Equidistant map. Also, Web Mercator cannot display the poles, so the basemap is clipped beyond the 85th parallel, leaving a blank area on the map.

    The topographic basemap is not suitable for your polar map, so you will find a suitable one.

  7. NOSatisfiedControl panel, right-clicktopographicaland chooseRemove.
  8. NOCatalogcontrol panel, clickPortalguide and clickliving atlasEyelash.

    Choose the right projection (15)

  9. NOSearch forBar Typepolar Base mapand pressureEnter.
  10. In the search results, right-clickBase of the Arctic Oceanand chooseAdd to current map.

    Choose the right projection (16)

    The map updates to show the new basemap, covering the portion of the earth north of the 50th parallel.

    Choose the right projection (17)

Find the northernmost magnetic pole

You will then use your map to measure the distances between true north and the moving magnetic north pole to determine the year they were closest.

  1. Make sure of this in the toolbar under the mapPhotothe button is highlighted.

    Choose the right projection (18)

    Optimization makes it easier for you to measure features.

  2. On the ribbon, click the buttonMapEyelash. In theAdviceclick groupMeasure.

    Ismeasure the distanceA window will appear at the top of the map.

    Choose the right projection (19)

  3. Click on the marked pointNorth Poleand click on the marked point2020.

    Choose the right projection (20)

    Advice:

    shutCor middle mouse button to scroll the map without disabling the measure tool.

    The tool reports a distance of 403.1 kilometers (250.47 miles).

  4. Press on the keyboardEscto delete the measurement.
  5. Measure the distance between the True North Pole and some previous locations of the Magnetic North Pole.

    Magnetic north was closest to true north in 2018 when it was 394.16 kilometers (244.92 miles) away. It is now heading south towards Russia.

You can make actual distance measurements on this map because it uses an equidistant projection. However, no projection can preserve all distances. HeAzimuth equidistantThe projection only preserves the distance and direction of the center. Therefore, measurements from the North Pole are true, but measurements between other locations on this map are inaccurate.

Measure geodetic and planar distances

The measurements you've taken so far have been flat. Level distances are like measuring with a ruler on a paper map. Geodetic distances are like measuring the surface of a globe with a string. You then compare planar and geodetic measurements between the magnetic north poles of 1590 and 2020.

  1. PressEscto delete your current measurement.
  2. Measure between the marked points1590and the marked point2020.

    Choose the right projection (21)

    The reported distance between these two locations is 1,758.73 kilometers (1,092.82 miles). However, the only precise plane distances that can be made on this map are from the center point. To find accurate distances between other places, you need to make geodetic measurements.

  3. PressEsc. NOmeasure the distancewindow, clickAwaymenu and selectgeodesic.

    Choose the right projection (22)

  4. Measure again the distance between the poles of 1590 and 2020.

    This time the reported distance is 1,866.63 kilometers (1,159.87 miles). The geodetic distance is more than 100 kilometers greater than the flat distance.

  5. closemeasure the distanceVentana.

Geodetic distances ignore the map projection and provide an actual distance. Flat distances are only true if the map uses a distance-preserving projection, and only up to specified points or along specified lines.

The projected coordinate system you chose for this map was already centered on the North Pole, which is where you wanted to measure. But what if you want to measure from a different point?

Change a projected coordinate system

You will then change the existing coordinate system to center it on magnetic north 1590 so that measurements can be taken from that point.

  1. Zoom to labeled point1590and click on it.

    IsLongjBroadare listed in the pop-up window. Pointer coordinates can also be read from the toolbar below the map.

    Choose the right projection (23)

  2. Close the popup.
  3. open thiscard propertieswindow and click the buttoncoordinate systemEyelash.
  4. NOAvailable XY coordinate systemsThe current coordinate system should be highlighted in the list.

    ENorth Pole Azimuthal Equidistantis not highlighted, use theSearch forcash to find it.

  5. The right mouse buttonNorth Pole Azimuthal Equidistant. Choosecopy and change.

    Choose the right projection (24)

    IsChange projected coordinate systemthe window appears. Here you can create a custom coordinate system with parameters that suit your needs.

  6. ForName, Typ1590 Equidistant Magnetic North Pole.

    Isprojectionis already configured forAzimuth equidistant. A projection and a projected coordinate system are not the same. A projection is a parameter on a projected coordinate system. Other parameters are a geographic coordinate system, a linear unit, and a number of parameters that depend on the selected projection (central meridian, scale factor, etc.).

    Use:

    Learn more about coordinate systems in the blog article.Coordinate Systems: What's the Difference?

    You'll adjust the parameters of this projected coordinate system so that it centers on the selected location instead of true north.

  7. ForMittelmeridian, Typ-111.831. Forlatitude of origin, Typ73.923.

    Choose the right projection (25)

    These are the values ​​that caught your eye in the pop-up window.

  8. give clickSave on computer.

    1590 Equidistant Magnetic North Polenow defined as theXY reallyCoordinate system for your map. Also included inhabitCategory of available coordinate systems.

    Choose the right projection (26)

    coordinate systems do nothabitCategory will not be saved. You then add it to a favorites folder so you can use it in future maps.

  9. Right-click the new custom coordinate system and selectAdd to favorites.
  10. Lowhabit, the right mouse button1590 Equidistant Magnetic North Poleand chooseAdd to favorites.

    Choose the right projection (27)

  11. Scroll to the top of the Coordinate Systems list and expandfavouritesgroup safe1590 Equidistant Magnetic North Poleis listed there.
    Use:

    Preferred coordinate systems are saved asprjfiles insideC:\Users\<your username>\AppData\Local\ESRI\ArcGISPro\Favorites.

  12. NOcard propertiesclick on the windowACCORDINGLYto confirm the change.

    The map is redrawn using the new projected coordinate system. It looks similar to the previous one, but the center of the map (if not the basemap) has been moved. The geodetic and planar measurements of the new point are now accurate.

  13. About itQuick access to the toolbar, CliqueCancelto reset the map to the projected coordinate system centered on True North.

    Choose the right projection (28)

  14. Save the project.

In ArcGIS, you can choose between planar orgeodeic measurements. But your card reader doesn't have this option; You just see a flat map on a screen or piece of paper. An equidistant projection is the right choice for this map so that everyone can correctly estimate the distance to the North Pole.

Sometimes you can't find a designed coordinate system that works for your map's purpose.ArcGIS Proallows you to modify any coordinate system to have parameters that best suit your needs. Next, you will learn how to create a custom projected coordinate system using the suggested parameters ofArcGIS Pro.

Mercator-Transversal-Universal (UTM)is a commonly used system for large-scale maps. If your map is narrower than 6° longitude, you can map it using a projected UTM coordinate system. The map you create below is narrow enough, but it doesn't fit well in an existing UTM zone.

In this tutorial module you will learn how to find the correct projected UTM coordinate system for an area of ​​interest and how to create a custom projected coordinate system to use when a standard UTM zone does not fit.

Find the right UTM zone

He wants to map the border between Finland and Russia. This will be a reference map intended to provide descriptive context for the border region. You want to use a conformal projection to show the shapes of features in their most recognizable form.

  1. Click the button at the top of the map viewHe mustTab to activate this map.

    Choose the right projection (29)

    This map currently uses the Web Mercator projection. While the Mercator projection is conformal, the Mercator mesh (the auxiliary Mercator sphere) is not. In addition, this projection drastically distorts the area and distances at higher latitudes.

    The white rectangle represents the area you want to map. Since this is a narrow part of the earth within 6° longitude, you can use a UTM zone. UTM projected coordinate systems are conformal and their distortion of other map properties is minimal.

    UTM divides the country into 60 zones. Next, you'll use a spatial filter to determine which UTM zone to use for your map.

  2. NOSatisfiedControl panel, double clickHe mustto open thecard propertiesVentana.
  3. About itcoordinate systemnext to the search barroom filterand clickDefine spatial filter.

    Choose the right projection (30)

  4. NOSpatial filter extensionclick on the windowlight line map.

    low valuesselected extensionupdate to match the extension oflight line mapcapacity

    Choose the right projection (31)

  5. give clickUse.

    IsAvailable XY coordinate systemsThe list is filtered to only include coordinate systems with extents that overlap your map.

  6. Expand the listProjected coordinate system,UTM,WG 1984, Ofnorthern hemisphere.

    Choose the right projection (32)

    There are two UTM zones for the area you wish to map, 35N and 36N, and you cannot tell from this list which zone is better.

  7. give clickCancelclosecard propertiesVentana.

    Next, you'll add a layer to your map to display the UTM raster.

  8. NOCatalogcontrol panel, clickPortalTab and clickliving atlas.
  9. Type in the search barUTM classand pressureEnter.
  10. In the search results, right-click theUTM World GridFeature Layer and selectAdd to current map.

    Choose the right projection (33)

  11. NOSatisfiedControl panel, right-clickWorld_UTM_Gridand chooselabel.

    The border between Finland and Russia lies on the border of two UTM zones: 35 and 36.

    Choose the right projection (34)

    UTM projection coordinate systems minimize distortion to reasonable levels, but only within their zonal ranges. Neither zone 35 nor zone 36 will provide this buff to the map area.

  12. NOSatisfiedControl panel, right-clickWorld_UTM_Gridand chooseRemove.

The World_UTM_Grid layer confirmed that the best option for this map is a custom coordinate system. You will then create one for that region.

Create a custom projected coordinate system

ArcGIS ProYou can propose new custom projected coordinate systems based on two criteria: warp property and map extent.

  1. NOSatisfiedControl panel, double clickHe mustto open thecard propertiesVentana.
  2. About itcoordinate systemtab, clickAdd coordinate systempress and selectNew projected coordinate system proposed.

    Choose the right projection (35)

    A new window appears.

  3. ForCoordinate system name, TypFinland-Russia border. LeaveGeographic coordinate systemadapted toWG 1984.

    Choose the right projection (36)

  4. Lowreceived an extension, Cliquelight line map.

    low valuesselected extensionupdate to match the extent of the map netline layer.

    Choose the right projection (37)

  5. Forprojection property, chooseaccordingly.

    The parameters of the new custom projected coordinate system are displayed inResultCrate.

    Choose the right projection (38)

    Isprojectionis set toMercator-Transversal-NGA 2014. That is avariantthe transverse Mercator projection used by UTM zone maps.

    Use:

    Transverse Mercator is a common projection used by UTM coordinate systems and some State Plate coordinate systems. The Transverse Mercator NGA 2014 is a variant of this projection with the added benefit of being able to show a larger portion of the world.

    IsMittelmeridianjlatitude of originThe parameters are taken from the center of the map neatline rectangle.

    Isthis fakemoves the origin point of the coordinate system away from the map area to ensure that no coordinates have negative values. Hescaling factorminimizes distortion throughout the 6° zone.

  6. give clickSave on computer.
  7. Lowhabit, the right mouse buttonFinland-Russia borderand chooseAdd to favorites.

    Choose the right projection (39)

  8. NOcard propertiesclick on the windowACCORDINGLYto confirm the change.

    The map is redrawn using the new projected coordinate system.

  9. NOSatisfiedControl panel, right-clickNational Geographic world mapand choosezoom to level.

    The new projected coordinate system distorts shapes far from its central meridian (29.9°E).

    Choose the right projection (40)

    Although this map can depict the entire world, it is only suitable for mapping areas in the center of this coordinate system, within 3° of its central meridian.

  10. expand tolight line mapcapacity

    The image below shows a comparison of the map in the new custom projected coordinate system and Web Mercator.

    Choose the right projection (41)

    In the custom coordinate system, the clean-edged polygon shape is a trapezoid instead of a rectangle. Its northern edge is shorter than the southern edge. The rectangle in Web Mercator is misleading: on Earth, these lines are not equal in length. The new projection shows them more accurately.

    The two maps shown above are drawn at the same scale: from 1 million to 20 million. But that scale doesn't make sense on the Web Mercator map because the range distortions are too extreme. The distortion on the Transverse Mercator map is small enough to go unnoticed, and more accurate measurements can be made on this map.

Earlier in this tutorial, you learned how to change coordinate systems. How could you change an existing UTM coordinate system to center it on the Russian-Finnish border? How could you change the Equal Earth projection from the beginning of this tutorial to better show the Pacific Ocean?

Advice:

Copy and change any zone coordinate system UTM WGS 1984. Change the central meridian to 29.9.

Copy and modify the Equal Earth coordinate system. Change the central meridian to 160°W or something similar.

In this tutorial, you learned a few techniques and explored resources to help you choose an appropriate map projection:

  • See theQuick notes on map projections in ArcGISChart.
  • Read the ArcGIS help documentation forcompatible map projections.
  • Perform keyword searches and spatial filtersArcGIS Pro.
  • Copy and change existing projected coordinate systems toArcGIS Pro.
  • AccessUTM classreference layerArcGIS Living Atlas of the World.
  • Create a custom projected coordinate system inArcGIS Prowith a property of extension and projection.

Take a look at the cards you see on the web, in the news or in apps. Do they use an appropriate projection? Are your distance and area measurements accurate?

Ignoring your choice of map projection can skew your data and mislead your map readers. However, if you spend some time looking for a properly designed coordinate system, you will create a map that clearly and accurately presents your data and messages.

For more cartography tutorials, visitIntroduction to cartographybook page.

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