Introducing Coordinate Systems and Map Projections

Introduction to Coordinate Systems and Map Projections

• Malia Kennedy and I will be discussing coordinate systems and map projections

• We are part of the projection engine team at ESRI, working with coordinate systems and map projections.

• In this section, we will address a common problem when working with GIS data - data not lining up due to coordinate system issues.

"We deal with coordinate systems, map projections, and transformations."

Problem with Data Alignment

• Malia shows an orthophoto image of Palm Springs area in ArcGIS Pro.

• She adds a polygon layer to mark the Palm Springs town border.

• When she turns on the polygon layer, nothing shows up.

• Zooming out, she notices that the polygon layer appears to be in the wrong location.

• The misalignment between the data suggests a problem with the coordinate system or missing transformation.

"Data doesn't line up due to coordinate system or missing transformation."

Main Sections of the Talk

• The talk will cover three main sections: coordinate systems, map projections, and transformations.

• General information about coordinate systems and their purpose.

• Specific details about map projections and the algorithms used.

• Understanding transformations and their role in aligning data.

"We will discuss coordinate systems, map projections, and transformations."

Geographic and Projected Coordinate Systems

• There are two types of supported horizontal coordinate systems: geographic and projected.

• A geographic coordinate system is based on a 3D model of the Earth, using longitude and latitude measurements.

• Projected coordinate systems use linear units, such as x, y, or eastings and northings.

• Geographic coordinate systems provide information about distance, location, and direction.

"Geographic coordinate systems are based on the Earth's 3D model, while projected coordinate systems use linear units."

Understanding the Parts of a Coordinate System

• A coordinate system consists of several components: prime meridian, angular unit, datum, projection, and linear unit.

• The datum is based on a sphere or ellipsoid, while the projection uses an algorithm.

• Coordinate systems can be specified using well-known IDs or text strings.

• Well-known text provides detailed information about each component of the coordinate system.

"A coordinate system includes components like datum, projection, and linear unit."

Well-Known IDs and Text for Coordinate Systems

• Well-known IDs (wkids) are numeric codes assigned by EPSG (European Petroleum Survey Group).

• WKIDs below 32767 are defined by EPSG, while higher numbers are defined by ESRI.

• Well-known text provides detailed information about the coordinate system components.

• In ArcGIS software, you can search and specify coordinate systems using WKIDs or text.

"Well-known IDs and text are used to specify coordinate systems in ArcGIS software."

Defined Projection Tool for Updating Metadata

• The Defined Projection tool is used to update the metadata of a data set.

• Overwriting the metadata with an incorrect coordinate system can cause data misalignment.

• When defining a projection, it is important to ensure the correct coordinate system is used.

"The Defined Projection tool updates metadata and must be used carefully to avoid data misalignment."

Introduction to Coordinate Systems and Map Projections

• Coordinate systems and map projections are a fundamental part of working with GIS data.

• They help us accurately represent the shape and location of objects on the Earth's surface.

• In this video, we will learn about different coordinate systems and map projections and how they are used in the field of GIS.

"Coordinate systems and map projections are fundamental in working with GIS data."

Vertical Coordinate Systems

• Vertical coordinate systems determine the height or depth values of objects on the Earth's surface.

• There are two types of vertical coordinate systems: geometric models and gravity-related systems.

• Geometric models use an ellipsoidal surface to represent the Earth's shape.

• Gravity-related systems are based on the Earth's gravity field and are often used for tidal levels.

"Vertical coordinate systems determine the height or depth values on the Earth's surface."

Geometric Model of the Earth

• Geometric models represent the Earth's surface as a lumpy and bumpy ellipsoid.

• They fit well everywhere but may not be as smooth as the Earth's surface.

• These models are commonly used in vertical coordinate systems.

"Geometric models represent the Earth's surface as a lumpy and bumpy ellipsoid."

Gravity-Related Vertical Coordinate Systems

• Gravity-related vertical coordinate systems are based on the Earth's gravity field.

• They use a geopotential surface called the geoid, which is a complex shape affected by what is underneath the ground.

• These systems often have a file of offsets between the geoid and the geometric model to account for the differences.

"Gravity-related systems use a geoid, a complex shape affected by what is underneath the ground."

Components of a Vertical Coordinate System

• A vertical coordinate system consists of several components: datum, vertical shift, direction, and linear unit.

• The datum determines whether the vertical coordinate system uses the geometric model or a gravity-related surface.

• The direction parameter specifies whether the Z values are positive up or positive down.

• The vertical shift allows for applying an offset to an existing coordinate system, useful for local adjustments.

"A vertical coordinate system includes a datum, vertical shift, direction, and linear unit."

Introduction to Map Projections

• Map projections convert the Earth's curved surface into a 2D representation.

• There are various map projections available, each with its own unique algorithm.

• Map projections are necessary because it is impossible to flatten the Earth's surface without distortion.

"Map projections convert the Earth's curved surface into a 2D representation."

Different Types of Map Projections

• There are numerous map projections available, including Albers equal-area conic, stereographic, azimuthal equidistant, and Mercator.

• Each projection has its own strengths and weaknesses, depending on the purpose of the map.

• For example, Albers equal-area conic preserves relative areas, while stereographic preserves angles.

"Each map projection has its own strengths and weaknesses."

Choosing the Right Map Projection

• The best map projection depends on the specific needs and purpose of the map.

• Albers equal-area conic is suitable for preserving areas, while stereographic is better for preserving angles.

• Cylindrical projections like transverse Mercator work well for topographic maps, while azimuthal equidistant projections maintain directions and distances from a central point.

"The best map projection depends on the specific needs of the map."

Introducing Coordinate Systems and Map Projections

• Azimuthal projection is good for polar areas and hemispheres.

• Different types of projections include stereographic, Weil equidistant, equal area, and orthographic.

• Pseudo cylindrical projections are also commonly used.

• Most of these projections are equal area.

"In like more of a hemisphere for half, the world then azimuthal projection not only is about good for polar areas but it could also be good for a hemisphere."

Examples of Different Map Projections

• Examples include listed projections such as stereographic, Weil equidistant, equal area, orthographic, and pseudo cylindrical.

• Stereographic projection maintains shapes.

• Weil equidistant distance through the center.

• Orthographic projection looks like a satellite view.

• Most of the listed projections are equal area.

• Examples of specific projections shown are HEALPix and Eckert.

"Most of these are equal area so for instance here's two of them the one on the left is HEALPix projection from last year Cody fourth on the right is another older one called Eckert for compromise projections..."

• "Equal area or orthographic which at orthographic is actually like if you had a satellite what it looks like for this kind of light you're working for world."

Understanding Coordinate System Transformations

• The project tool is used to convert data between different coordinate systems.

• The tool can convert between different projected coordinate systems (PCS) and geographic coordinate systems (GCS).

• Reprojection is used to convert data within the same GCS.

• Transformation is used when changing the GCS.

• A transformation involves unprojecting and reprojecting data.

"The project tool is what actually converts your data between different coordinate systems... if we're starting on the left side with a1 and the PCS the first thing we do is we unproject the long lat values... then we project forward into a2 the output PCS."

Transforming Data in GIS

• Data transformation is needed to align data with an appropriate base map.

• Older GCS might not align properly with newer ones.

• Transformations involve changing the data and the geographic coordinate system.

"So the final section of transformations... so why do we need to transform our data... an example is that our base map is an older GCS called 8050 European date of 1950 and we've got a route and WGS84."

Understanding Datum Transformations

• Older datums were designed for specific local areas and might not align with the entire world.

• These datums need to be converted into world-based or more recent coordinate systems.

"Older datums and what I like to call local datums when they redefine people only cared about the local area they weren't trying to match the entire world."

Geographic and Vertical Transformations

• Geographic transformations convert between different geographic coordinate systems.

• Vertical transformations convert between different vertical coordinate systems.

• Transformations have specific extents and accuracies.

• The choice of transformation is influenced by the data and coordinate systems being used.

"We support Geographic or datum transformation it converts between the two geographic coordinate systems... right now between WGS 1984 and ED 1950 we have 24 different transformations that convert between the two of them."

Coordinate Systems and Map Projections

• Coordinate systems are a fundamental part of GIS data.

• New data is set up in coordinate systems using the arc GS coordinate systems data set.

• Each new release may have a few updates to the data setup.

• Desktop 10.7 and Pro 2.3 are already installed, and when Pro 2.4 is released, the same setup can be used.

• The data setup works for desktop, server, and Pro if installed per machine.

• If Pro is installed per user, a data setup also needs to be installed per user.

• The current data setup is around 1.6 gigabytes in size.

"Coordinate systems are a fundamental part of GIS data."

Issues with Coordinate Systems

• The orthophoto image uses the UTM zone 11n coordinate system.

• The coordinate system of the polygon data is unknown.

• As a result, the polygon data does not show up in the correct location.

• The extent of the polygon data has values that are less than one unit, which is unlikely.

• Assuming the data is in the WGS84 geographic coordinate system, the issue can be fixed.

"The issue is that the coordinate system of the polygon data is unknown."

Finding the Coordinate System

• To fix the issue, the Projection tool can be used.

• By selecting the polygon and specifying the coordinate system, the data will show up in the correct location.

• The coordinate system can be found by searching or browsing through existing coordinate systems.

• Favorites can also be used to quickly locate frequently used coordinate systems.

• The spatial filter can be applied to find coordinate systems based on specific coordinates.

"To fix the issue, the Projection tool can be used."

Exploring Coordinate Systems

• Using the spatial filter, coordinates can be manually entered to find matching coordinate systems.

• The units of the spatial filter can be changed to fit the desired input.

• The filter helps narrow down the available coordinate systems based on the given coordinates.

• Favorites folder on the coordinate systems window contains frequently used coordinate systems.

• Coordinate systems in the favorites folder are quickly accessible when selecting the data.

"The spatial filter helps narrow down the available coordinate systems."

Introduction to Coordinate Systems and Map Projections

• Geographic coordinate systems are used to express locations on the Earth's surface.

• There are different coordinate systems available, including specific ones for California.

• In addition to geographic coordinate systems, there are also projected coordinate systems.

"Geographic coordinate systems are the fundamental part of expressing locations on Earth's surface."

Filtering Coordinate Systems Based on Extents

• The coordinate system options can be filtered based on the desired extent.

• For example, if working on a project related to North America, the filter can be set to only show coordinate systems applicable to that region.

• The filters can be cleared to see all available coordinate system options.

"You can filter coordinate systems based on the extent you are working with, allowing you to narrow down the options."

Selecting and Customizing Coordinate Systems

• Various coordinate systems can be selected, including projected coordinate systems, geographic coordinate systems, and vertical coordinate systems.

• Custom coordinate systems can be used if they are not defined by Hazari or EPSG.

• The coordinate system parameters, such as name and units, can be specified during the selection process.

• Different projections and their variants are available to choose from, each with its own set of parameters.

"You can select and customize a wide range of coordinate systems, including both projected and geographic coordinate systems."

Lambert Conformal Conic Projection

• The Lambert conformal conic projection has two ways to specify the coordinate system: using a set of parameters or by specifying standard parallels and a scale factor.

• By using the specified parameters, one can define the coordinate system accurately.

"The Lambert conformal conic projection offers different ways to specify the coordinate system, allowing for flexibility in defining the projection accurately."

Using Coordinate System IDs and Transformations

• Instead of searching for coordinate systems, you can directly input the ID of the desired geographic coordinate system.

• The system will automatically search and add the specified coordinate system.

• Transformations can be specified to ensure alignment between different coordinate systems.

"You can input the ID of a geographic coordinate system to quickly add it, and specify transformations for aligning different coordinate systems."

Available resources for learning about coordinate systems and transformations

• EPSG has an online registry for looking up and searching coordinate systems and transformations

• EPSG also provides a guidance note for learning more about coordinate systems and transformations

• The guidance note is about 150 pages long and provides background information on the topic

• There is a public GitHub repository with documentation on coordinate systems that can be downloaded

• Margaret's book, "Lining Up Data in ArcGIS," is a useful resource for coordinate systems and transformations

"EPSG not only do they have this online registry where you can look up... transformations are available."

"There is a public GitHub repo with some documentation about the coordinate systems that you can download."

Determining the best transformations based on data extent and accuracy

• There is a PDF file called "Geographic_Transformations.pdf" that provides extensive information on transformations

• The PDF includes tables with information on transformation extents and accuracies

• Translations from EPSG registry are the most reliable source for transformation information

"There's a PDF file called 'Geographic_Transformations.pdf' that has humongous tables of stuff."

"So, when we sort that list, we take a look at your data extent and compare it against the transformation extents and the coordinate system extents."

Checking coordinate system and transformation in ArcGIS

• Check the coordinate system in Oracle first and verify it in ArcGIS using the measure tool

• By visualizing the data with a basemap in ArcGIS, you can double-check the correctness of the coordinate system

"Whatever works, so if it's working then that's perfectly good."

"This was the right thing to do."

Reprojecting data in ArcGIS Desktop and Pro

• When adding data in a different coordinate system, ArcGIS will reproject it to match the map or scene's coordinate system

• There might be a need for a transformation during the reprojection process

"Once you set up the map or scene's coordinate system, if you keep adding in more layers... we're going to reproject it to match whatever the map or scene is in."

"There might need to be a transformation."

Coordinate Systems and Map Projections

• Sometimes the transformation is not applied automatically.

• Desktop does not set a transformation automatically and a warning message appears.

• ArcGIS Pro also has a warning message, but it is turned off by default.

• In ArcGIS Pro, the transformation is usually already set.

• In ArcGIS Pro, the transformation list usually picks up the first transformation on the list, even if it covers more than the specific area being worked on.

"If you really rely on that or think people you work with should be worried relying on that, you could turn it on for them."

Changing Map Projections and Transformation

• Changing the base map can affect the transformation.

• When the base map covering the extent of the world is added to a map with data in a smaller area, ArcGIS Pro may switch to a transformation that covers the most possible data.

• There might be a bug or action item to ignore the base map when working with specific data.

"Normally that has a much bigger extent than the area you're interested in, and the guy in charge of the map side of both desktop and Pro said that we should really look at that."

Setting Default Options for New Maps and Scenes

• In ArcGIS Pro options, under applications, select map scene.

• Under "Settings - Set default options for new maps and new scenes," you can specify the default spatial reference.

• By checking the "Warn if the transformation between geographic coordinate systems is required to align data sources correctly" box, you will receive a warning if a transformation is required.

"So you cannot check that box and you will have that option in your pro."

Stack Exchange Resources and Questions

• On Stack Exchange and Stack Overflow, people ask questions about MapInfo and other GIS topics.

• There are answered questions and resources available to help with various GIS-related issues.

"There's all kinds of answered questions there, and people can ask about stuff like that, and someone will know pretty much."

Challenges with Separate Data Sets

• Having a separate data set for transformations is risky as customers may not realize they need to install it.

• If a transformation requires data in the separate data set and it is not installed, it will not show up in the transformation list.

• Users may not be aware of the transformations they should use if they are not displayed in the list.

"You might not even know that that's a transformation you should use because it's not showing up in the list."

Suggestions for Improving Data Set Installations

• There is a debate between making the core setup larger by adding more data or having a separate setup.

• Some suggest making the coordinate system setup a required installation.

• Currently, Pro prompts users to install the latest coordinate system update if they already have the setup.

"You kind of query, and then you can just hit to download it again and you can install it."

Ensuring Usable Transformations

• Esri checks if transformations are usable before displaying them in the list.

• This prevents users from selecting transformations that won't work with their data.

• However, usable transformations that are not installed may not be shown in the list.

"We do sort that list and if we check and make sure it's this a usable transformation or not, if it's not usable, it won't show up as a possibility."