{"id":270442,"date":"2018-07-24T11:00:02","date_gmt":"2018-07-24T18:00:02","guid":{"rendered":"http:\/\/www.esri.com\/arcgis-blog\/?post_type=blog&p=270442"},"modified":"2022-03-14T12:29:24","modified_gmt":"2022-03-14T19:29:24","slug":"define-projection-or-project-coordinate-systems-in-arcgis","status":"publish","type":"blog","link":"https:\/\/www.esri.com\/arcgis-blog\/products\/arcgis-pro\/mapping\/define-projection-or-project-coordinate-systems-in-arcgis","title":{"rendered":"Define Projection or Project?"},"author":7411,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","format":"standard","meta":{"_acf_changed":false,"_searchwp_excluded":""},"categories":[22941],"tags":[25591,26451,169802,169792],"industry":[],"product":[36561,36991],"class_list":["post-270442","blog","type-blog","status-publish","format-standard","hentry","category-mapping","tag-arcgis-desktop","tag-cartography","tag-coordinate-systems","tag-projections","product-arcgis-pro","product-arcgis-desktop"],"acf":{"short_description":"The Define Projection tool and Project tool are often confused. Learn how to properly use them to fix your data.","flexible_content":[{"acf_fc_layout":"content","content":"

There’s something wrong with your data’s coordinate system, but what to do? Which tool is the one for you?<\/p>\n

\u2022 If your data doesn’t have a coordinate system, or you suspect it has the wrong one, you want Define Projection<\/a>.
\n\u2022 If your data already has a coordinate system but you wish to convert it into a different one, you want Project<\/a>.<\/p>\n

Here’s an analogy:
\nYou bought some things online.<\/p>\n"},{"acf_fc_layout":"image","image":{"ID":271222,"id":271222,"title":"receipt2","filename":"receipt2.png","filesize":5223,"url":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2018\/07\/receipt2.png","link":"https:\/\/www.esri.com\/arcgis-blog\/products\/arcgis-pro\/mapping\/define-projection-or-project-coordinate-systems-in-arcgis\/receipt2","alt":"receipt totaling $44","author":"7411","description":"","caption":"","name":"receipt2","status":"inherit","uploaded_to":270442,"date":"2018-07-06 21:39:54","modified":"2018-07-06 21:43:56","menu_order":0,"mime_type":"image\/png","type":"image","subtype":"png","icon":"https:\/\/www.esri.com\/arcgis-blog\/wp-includes\/images\/media\/default.png","width":320,"height":176,"sizes":{"thumbnail":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2018\/07\/receipt2.png","thumbnail-width":213,"thumbnail-height":117,"medium":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2018\/07\/receipt2.png","medium-width":320,"medium-height":176,"medium_large":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2018\/07\/receipt2.png","medium_large-width":320,"medium_large-height":176,"large":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2018\/07\/receipt2.png","large-width":320,"large-height":176,"1536x1536":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2018\/07\/receipt2.png","1536x1536-width":320,"1536x1536-height":176,"2048x2048":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2018\/07\/receipt2.png","2048x2048-width":320,"2048x2048-height":176,"card_image":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2018\/07\/receipt2.png","card_image-width":320,"card_image-height":176,"wide_image":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2018\/07\/receipt2.png","wide_image-width":320,"wide_image-height":176}},"image_position":"center","orientation":"horizontal","hyperlink":""},{"acf_fc_layout":"content","content":"

Your receipt shows that you paid $44. But your credit card was charged $45.22. That\u2019s not cool – where did that $1.22 go? Why doesn\u2019t the data match up?<\/p>\n

You think perhaps there\u2019s something wrong with the currency. You live in Australia, so you want to make sure those dollar amounts are in AUD. You run the Define Currency<\/em> tool with your price list and choose Australian Dollars.<\/p>\n"},{"acf_fc_layout":"image","image":{"ID":270602,"id":270602,"title":"define","filename":"define.png","filesize":11880,"url":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/define.png","link":"https:\/\/www.esri.com\/arcgis-blog\/products\/arcgis-pro\/mapping\/define-projection-or-project-coordinate-systems-in-arcgis\/define","alt":"","author":"7411","description":"","caption":"","name":"define","status":"inherit","uploaded_to":270442,"date":"2018-07-06 18:05:53","modified":"2018-07-06 18:07:09","menu_order":0,"mime_type":"image\/png","type":"image","subtype":"png","icon":"https:\/\/www.esri.com\/arcgis-blog\/wp-includes\/images\/media\/default.png","width":300,"height":203,"sizes":{"thumbnail":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/define.png","thumbnail-width":213,"thumbnail-height":144,"medium":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/define.png","medium-width":300,"medium-height":203,"medium_large":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/define.png","medium_large-width":300,"medium_large-height":203,"large":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/define.png","large-width":300,"large-height":203,"1536x1536":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/define.png","1536x1536-width":300,"1536x1536-height":203,"2048x2048":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/define.png","2048x2048-width":300,"2048x2048-height":203,"card_image":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/define.png","card_image-width":300,"card_image-height":203,"wide_image":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/define.png","wide_image-width":300,"wide_image-height":203}},"image_position":"center","orientation":"horizontal","hyperlink":""},{"acf_fc_layout":"content","content":"

You look at your new price list and discover that the tool did not solve your problem. The total still doesn’t match your credit card statement:<\/p>\n\n\n\n\n\n\n
Shoes<\/td>\n$24.00 AUD<\/td>\n<\/tr>\n
Hat<\/td>\n$12.00 AUD<\/td>\n<\/tr>\n
Water Bottle<\/td>\n$8.00 AUD<\/td>\n<\/tr>\n
Total<\/strong><\/td>\n$44.00 AUD<\/strong><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Why didn’t Define Currency<\/em> work?
\nYou should have taken a closer look at your metadata:<\/p>\n"},{"acf_fc_layout":"image","image":{"ID":270742,"id":270742,"title":"receipt","filename":"receipt-1.png","filesize":14014,"url":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2018\/07\/receipt-1.png","link":"https:\/\/www.esri.com\/arcgis-blog\/products\/arcgis-pro\/mapping\/define-projection-or-project-coordinate-systems-in-arcgis\/receipt-2","alt":"the receipt shows an address in Canada","author":"7411","description":"","caption":"","name":"receipt-2","status":"inherit","uploaded_to":270442,"date":"2018-07-06 18:29:16","modified":"2018-07-06 18:38:55","menu_order":0,"mime_type":"image\/png","type":"image","subtype":"png","icon":"https:\/\/www.esri.com\/arcgis-blog\/wp-includes\/images\/media\/default.png","width":319,"height":301,"sizes":{"thumbnail":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2018\/07\/receipt-1.png","thumbnail-width":213,"thumbnail-height":200,"medium":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2018\/07\/receipt-1.png","medium-width":277,"medium-height":261,"medium_large":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2018\/07\/receipt-1.png","medium_large-width":319,"medium_large-height":301,"large":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2018\/07\/receipt-1.png","large-width":319,"large-height":301,"1536x1536":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2018\/07\/receipt-1.png","1536x1536-width":319,"1536x1536-height":301,"2048x2048":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2018\/07\/receipt-1.png","2048x2048-width":319,"2048x2048-height":301,"card_image":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2018\/07\/receipt-1.png","card_image-width":319,"card_image-height":301,"wide_image":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2018\/07\/receipt-1.png","wide_image-width":319,"wide_image-height":301}},"image_position":"center","orientation":"horizontal","hyperlink":""},{"acf_fc_layout":"content","content":"

You read the fine print on your receipt and discover that the company you bought the stuff from is in Canada. Those prices were in Canadian dollars. The correct workflow for your problem is:
\n1.<\/strong> Run the Define Currency <\/em>tool and choose Canadian dollars:<\/p>\n"},{"acf_fc_layout":"image","image":{"ID":270752,"id":270752,"title":"define","filename":"define-1.png","filesize":11808,"url":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/define-1.png","link":"https:\/\/www.esri.com\/arcgis-blog\/products\/arcgis-pro\/mapping\/define-projection-or-project-coordinate-systems-in-arcgis\/define-2","alt":"","author":"7411","description":"","caption":"","name":"define-2","status":"inherit","uploaded_to":270442,"date":"2018-07-06 18:30:36","modified":"2018-07-06 18:30:53","menu_order":0,"mime_type":"image\/png","type":"image","subtype":"png","icon":"https:\/\/www.esri.com\/arcgis-blog\/wp-includes\/images\/media\/default.png","width":300,"height":203,"sizes":{"thumbnail":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/define-1.png","thumbnail-width":213,"thumbnail-height":144,"medium":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/define-1.png","medium-width":300,"medium-height":203,"medium_large":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/define-1.png","medium_large-width":300,"medium_large-height":203,"large":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/define-1.png","large-width":300,"large-height":203,"1536x1536":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/define-1.png","1536x1536-width":300,"1536x1536-height":203,"2048x2048":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/define-1.png","2048x2048-width":300,"2048x2048-height":203,"card_image":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/define-1.png","card_image-width":300,"card_image-height":203,"wide_image":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/define-1.png","wide_image-width":300,"wide_image-height":203}},"image_position":"center","orientation":"horizontal","hyperlink":""},{"acf_fc_layout":"content","content":"

Your new price list looks like this:<\/p>\n\n\n\n\n\n\n
Shoes<\/td>\n$24.00 CAD<\/td>\n<\/tr>\n
Hat<\/td>\n$12.00 CAD<\/td>\n<\/tr>\n
Water Bottle<\/td>\n$8.00 CAD<\/td>\n<\/tr>\n
Total<\/strong><\/td>\n$44.00 CAD<\/strong><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

2.<\/strong> Run the Convert Currency<\/em> tool and choose Australian:<\/p>\n"},{"acf_fc_layout":"image","image":{"ID":270762,"id":270762,"title":"project","filename":"project.png","filesize":19724,"url":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/project.png","link":"https:\/\/www.esri.com\/arcgis-blog\/products\/arcgis-pro\/mapping\/define-projection-or-project-coordinate-systems-in-arcgis\/project","alt":"The Project tool pretending to be \"Convert Currency\"","author":"7411","description":"","caption":"","name":"project","status":"inherit","uploaded_to":270442,"date":"2018-07-06 18:32:03","modified":"2018-07-06 18:32:26","menu_order":0,"mime_type":"image\/png","type":"image","subtype":"png","icon":"https:\/\/www.esri.com\/arcgis-blog\/wp-includes\/images\/media\/default.png","width":299,"height":301,"sizes":{"thumbnail":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/project.png","thumbnail-width":199,"thumbnail-height":200,"medium":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/project.png","medium-width":259,"medium-height":261,"medium_large":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/project.png","medium_large-width":299,"medium_large-height":301,"large":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/project.png","large-width":299,"large-height":301,"1536x1536":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/project.png","1536x1536-width":299,"1536x1536-height":301,"2048x2048":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/project.png","2048x2048-width":299,"2048x2048-height":301,"card_image":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/project.png","card_image-width":299,"card_image-height":301,"wide_image":"https:\/\/www.esri.com\/arcgis-blog\/app\/uploads\/2020\/07\/project.png","wide_image-width":299,"wide_image-height":301}},"image_position":"center","orientation":"horizontal","hyperlink":""},{"acf_fc_layout":"content","content":"

Now the price list looks like this:<\/p>\n\n\n\n\n\n\n
Shoes<\/td>\n$24.37 AUD<\/td>\n<\/tr>\n
Hat<\/td>\n$12.33 AUD<\/td>\n<\/tr>\n
Water Bottle<\/td>\n$8.22 AUD<\/td>\n<\/tr>\n
Total<\/strong><\/td>\n$45.22 AUD<\/strong><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

And it matches your credit card statement correctly. Mystery solved.<\/p>\n

The workflow is the same when your geographic data doesn’t line up. <\/strong><\/p>\n

You need to know \u2013 and define \u2013 what the original coordinate system is before you can convert it into a different one. If you start with the wrong coordinate system, you will be using the wrong transformation, and the result will have the wrong coordinate values.<\/p>\n

Define Projection<\/strong>
\nIf your data is not drawing in the right place, it may not have a coordinate system defined yet, or it may have the wrong one. You need to Define Projection<\/em> before you can continue.<\/p>\n

\u2022 Check Layer Properties<\/em> > Source <\/em>> Spatial Reference<\/em> to find out what coordinate system your data is in. If it says \u201cUnknown Coordinate System\u201d you definitely want to use the Define Projection<\/em> tool.<\/p>\n

\u2022 The Define Projection tool will not<\/strong> make a copy of your data. It will only change the metadata of the existing dataset. If you run this tool and guess the wrong coordinate system, you\u2019ll make things worse. But the good news is that none of your actual coordinate values have been changed, so if you are able to find out the right coordinate system, and you run the tool again, your data will be fixed.<\/p>\n

Project<\/strong>
\nOnce you have defined the correct coordinate system, you should be good to go. ArcGIS Pro and ArcMap will project-on-the-fly to make your data draw with whatever coordinate system your map is using, and it will draw in the right place. However, if you want to make sure that all of the data you are using in a project has the same coordinate system \u2013 for consistency and accuracy in analysis and editing, or to minimize reprojections in a project or layer \u2013 then you should run the Project <\/em>tool. This will make a copy of your data and convert it into a different coordinate system.<\/p>\n

\u2022 Note that raster datasets should be converted using the Project Raster<\/a> tool instead.<\/p>\n

\u2022 Sometimes (when the datums are different) a Transformation <\/strong>is required. If you don\u2019t know which transformation to choose, the first one in the list is your safest choice.<\/p>\n

What\u2019s the difference between a Coordinate System and a Projection anyways?<\/strong><\/em>
\nDon\u2019t be deceived by the names of these tools \u2013 Project and Define Projection \u2013 you can use either of them without ever using a projection. Why? Because they are actually defining and converting Coordinate Systems<\/em>.<\/p>\n

\u2022 What is a Geographic Coordinate System (GCS)?<\/em>
\nThis is the imaginary grid you are drawing over the earth\u2019s surface in order to define where things are. The main ingredient of a GCS is the Datum<\/strong>. The same latitude and longitude values will draw in different places on the earth when using a different GCS. Your data needs a GCS before it can know where to draw.<\/p>\n

\u2022 What is a Projected Coordinate System (PCS)?<\/em>
\nThis is a combination of a GCS + a Projection. The GCS tells your data where to draw on the earth, and the projection tells the map how to distort the earth onto a flat surface. Every PCS contains a GCS.<\/p>\n

Here\u2019s the recipe for a Projected Coordinate System:
\nProjected Coordinate System (PCS)<\/strong>
\n1 Linear Unit (e.g. Meters)<\/em>
\n1 Projection (e.g. Transverse Mercator, Stereographic, etc.)<\/em>
\nVarious projection parameters (depending on the chosen Projection)<\/em>
\n1 Geographic Coordinate system (GCS)<\/strong>
\n1 Angular unit (e.g. Degree)<\/em>
\n1 Prime meridian (e.g. Greenwich)<\/em>
\n1 Datum (e.g. WGS 1984)<\/em>
\n1 Spheroid<\/p>\n

To learn more, read these other articles that I have written about coordinate systems:<\/p>\n