{"id":528,"date":"2022-02-10T20:45:06","date_gmt":"2022-02-11T01:45:06","guid":{"rendered":"https:\/\/pressbooks.library.upei.ca\/geospatialhumanities\/?post_type=chapter&p=528"},"modified":"2022-02-10T20:45:24","modified_gmt":"2022-02-11T01:45:24","slug":"part-ii-b-setting-the-projects-coordinate-reference-system","status":"publish","type":"chapter","link":"https:\/\/pressbooks.library.upei.ca\/geospatialhumanities\/chapter\/part-ii-b-setting-the-projects-coordinate-reference-system\/","title":{"raw":"Part II B: Setting the Project\u2019s Coordinate Reference System","rendered":"Part II B: Setting the Project\u2019s Coordinate Reference System"},"content":{"raw":"Since Earth is spherical in shape, mapmakers use something called a map projection to flatten the globe onto a flat surface in order to make a map. A Coordinate Reference System (CRS) defines a map projection. So, we choose a CRS, and it sets a map projection for our project.\r\n\r\nPerhaps one of the best-known map projections is the Mercator projection, which was developed in the sixteenth century.\r\n\r\nHere is our OpenStreetMap layer set to the default CRS\u2014EPSG:3857 WGS 84 \/ Pseudo-Mercator, which is a Mercator projection.\r\n\r\n[caption id=\"attachment_529\" align=\"aligncenter\" width=\"706\"]\"Figure Figure 1.28<\/strong>[\/caption]\r\n\r\n
Fact:<\/strong> EPSG stands for European Petroleum Survey Group, which developed the CRS standards in the 1980s while conducting oil exploration in Europe.<\/div>\r\n \r\n\r\nWhile the Mercator projection succeeds in displaying the spherical globe on a flat surface, it distorts the size of the world\u2019s landmasses. Areas far away from the equator, such as Canada, are inaccurately enlarged in relation to areas nearer to the equator, which remain accurate.\r\n\r\nIn the past century or so, mapmakers have been trying to create alternatives to the Mercator projection. The goal is to create ones that avoid some of the distortion that the Mercator projection causes.\r\n\r\nWe will set the CRS of our project to one that accurately represents Prince Edward Island, for that is our area of focus. If we were mapping another region, such as the contiguous United States, we could set our CRS to one that is specific to that part of the world.\r\n\r\nTo set our project\u2019s Coordinate Reference System:\r\n
    \r\n \t
  • Click Project, then Properties, then CRS.<\/li>\r\n<\/ul>\r\n[caption id=\"attachment_530\" align=\"aligncenter\" width=\"552\"]\"Figure Figure 1.29<\/strong>[\/caption]\r\n\r\n[caption id=\"attachment_531\" align=\"aligncenter\" width=\"977\"]\"Figure Figure 1.30<\/strong>[\/caption]\r\n\r\nQGIS has a small preview screen that shows you to which area your CRS is tailored. Currently, the CRS is set to the default\u2014EPSG:3857 - WGS 84 \/ Pseudo-Mercator.\r\n
      \r\n \t
    • Type 2954 into the Filter search box.<\/li>\r\n \t
    • In the Predefined Reference System area, click to highlight the search result called NAD83(CSRS) \/ Prince Edward Isl. Stereographic (NAD83). It has the Authority ID called EPSG:2954.<\/li>\r\n \t
    • Click OK.<\/li>\r\n<\/ul>\r\n[caption id=\"attachment_532\" align=\"aligncenter\" width=\"977\"]\"Figure Figure 1.31<\/strong>[\/caption]\r\n\r\nThe following window will pop up. It asks us to select a transformation.\r\n
        \r\n \t
      • Select the first transformation option and click OK.<\/li>\r\n<\/ul>\r\n[caption id=\"attachment_533\" align=\"aligncenter\" width=\"977\"]\"Figure Figure 1.32<\/strong>[\/caption]\r\n\r\nWe had to choose a transformation because the default CRS of the OpenStreetMap layer is different than EPSG:2954, the one we just set for our project. QGIS will use the transformation setting we just chose to project the OpenStreetMap layer in the project\u2019s CRS. In fact, if we add any more map layers that have a CRS different than that of our project\u2019s CRS, QGIS will reproject these layers in the project\u2019s CRS too. This process has been termed \u201con-the-fly projection,\u201d and it is a strength of GIS software. On-the-fly projection will ensure that, notwithstanding a layer\u2019s default CRS, all layers that we add to QGIS will display according to the project\u2019s CRS. This is critical, for it ensures that there is consistency in how all the layers are presented.\r\n\r\nHere is the result of setting our project\u2019s CRS to EPSG:2954. Canada is much more accurate in size and shape, although the focal point has become Prince Edward Island.\r\n\r\n[caption id=\"attachment_534\" align=\"aligncenter\" width=\"977\"]\"Figure Figure 1.33<\/strong>[\/caption]\r\n\r\n
        Note:<\/strong> you can quickly view your project\u2019s CRS by looking to the bottom-right of the QGIS window.<\/div>\r\n\r\n[caption id=\"attachment_535\" align=\"aligncenter\" width=\"760\"]\"Figure Figure 1.34<\/strong>[\/caption]","rendered":"

        Since Earth is spherical in shape, mapmakers use something called a map projection to flatten the globe onto a flat surface in order to make a map. A Coordinate Reference System (CRS) defines a map projection. So, we choose a CRS, and it sets a map projection for our project.<\/p>\n

        Perhaps one of the best-known map projections is the Mercator projection, which was developed in the sixteenth century.<\/p>\n

        Here is our OpenStreetMap layer set to the default CRS\u2014EPSG:3857 WGS 84 \/ Pseudo-Mercator, which is a Mercator projection.<\/p>\n

        \"Figure
        Figure 1.28<\/strong><\/figcaption><\/figure>\n
        Fact:<\/strong> EPSG stands for European Petroleum Survey Group, which developed the CRS standards in the 1980s while conducting oil exploration in Europe.<\/div>\n

         <\/p>\n

        While the Mercator projection succeeds in displaying the spherical globe on a flat surface, it distorts the size of the world\u2019s landmasses. Areas far away from the equator, such as Canada, are inaccurately enlarged in relation to areas nearer to the equator, which remain accurate.<\/p>\n

        In the past century or so, mapmakers have been trying to create alternatives to the Mercator projection. The goal is to create ones that avoid some of the distortion that the Mercator projection causes.<\/p>\n

        We will set the CRS of our project to one that accurately represents Prince Edward Island, for that is our area of focus. If we were mapping another region, such as the contiguous United States, we could set our CRS to one that is specific to that part of the world.<\/p>\n

        To set our project\u2019s Coordinate Reference System:<\/p>\n

          \n
        • Click Project, then Properties, then CRS.<\/li>\n<\/ul>\n
          \"Figure
          Figure 1.29<\/strong><\/figcaption><\/figure>\n
          \"Figure
          Figure 1.30<\/strong><\/figcaption><\/figure>\n

          QGIS has a small preview screen that shows you to which area your CRS is tailored. Currently, the CRS is set to the default\u2014EPSG:3857 – WGS 84 \/ Pseudo-Mercator.<\/p>\n

            \n
          • Type 2954 into the Filter search box.<\/li>\n
          • In the Predefined Reference System area, click to highlight the search result called NAD83(CSRS) \/ Prince Edward Isl. Stereographic (NAD83). It has the Authority ID called EPSG:2954.<\/li>\n
          • Click OK.<\/li>\n<\/ul>\n
            \"Figure
            Figure 1.31<\/strong><\/figcaption><\/figure>\n

            The following window will pop up. It asks us to select a transformation.<\/p>\n

              \n
            • Select the first transformation option and click OK.<\/li>\n<\/ul>\n
              \"Figure
              Figure 1.32<\/strong><\/figcaption><\/figure>\n

              We had to choose a transformation because the default CRS of the OpenStreetMap layer is different than EPSG:2954, the one we just set for our project. QGIS will use the transformation setting we just chose to project the OpenStreetMap layer in the project\u2019s CRS. In fact, if we add any more map layers that have a CRS different than that of our project\u2019s CRS, QGIS will reproject these layers in the project\u2019s CRS too. This process has been termed \u201con-the-fly projection,\u201d and it is a strength of GIS software. On-the-fly projection will ensure that, notwithstanding a layer\u2019s default CRS, all layers that we add to QGIS will display according to the project\u2019s CRS. This is critical, for it ensures that there is consistency in how all the layers are presented.<\/p>\n

              Here is the result of setting our project\u2019s CRS to EPSG:2954. Canada is much more accurate in size and shape, although the focal point has become Prince Edward Island.<\/p>\n

              \"Figure
              Figure 1.33<\/strong><\/figcaption><\/figure>\n
              Note:<\/strong> you can quickly view your project\u2019s CRS by looking to the bottom-right of the QGIS window.<\/div>\n
              \"Figure
              Figure 1.34<\/strong><\/figcaption><\/figure>\n","protected":false},"author":31,"menu_order":6,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[48],"contributor":[],"license":[],"class_list":["post-528","chapter","type-chapter","status-publish","hentry","chapter-type-numberless"],"part":454,"_links":{"self":[{"href":"https:\/\/pressbooks.library.upei.ca\/geospatialhumanities\/wp-json\/pressbooks\/v2\/chapters\/528","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.library.upei.ca\/geospatialhumanities\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.library.upei.ca\/geospatialhumanities\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.library.upei.ca\/geospatialhumanities\/wp-json\/wp\/v2\/users\/31"}],"version-history":[{"count":2,"href":"https:\/\/pressbooks.library.upei.ca\/geospatialhumanities\/wp-json\/pressbooks\/v2\/chapters\/528\/revisions"}],"predecessor-version":[{"id":537,"href":"https:\/\/pressbooks.library.upei.ca\/geospatialhumanities\/wp-json\/pressbooks\/v2\/chapters\/528\/revisions\/537"}],"part":[{"href":"https:\/\/pressbooks.library.upei.ca\/geospatialhumanities\/wp-json\/pressbooks\/v2\/parts\/454"}],"metadata":[{"href":"https:\/\/pressbooks.library.upei.ca\/geospatialhumanities\/wp-json\/pressbooks\/v2\/chapters\/528\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.library.upei.ca\/geospatialhumanities\/wp-json\/wp\/v2\/media?parent=528"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.library.upei.ca\/geospatialhumanities\/wp-json\/pressbooks\/v2\/chapter-type?post=528"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.library.upei.ca\/geospatialhumanities\/wp-json\/wp\/v2\/contributor?post=528"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.library.upei.ca\/geospatialhumanities\/wp-json\/wp\/v2\/license?post=528"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}