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This post is for an outdated version of QGis (2.18). Find the latest version of this post (Version 3.30) here<\/a>.<\/div><\/div><\/p>\n\n\n\n

Thanks to the SRTM project we can access to a comprehensive world coverage of land elevation data. It\u00a0has\u00a0become\u00a0very\u00a0simple to\u00a0create one\u2019s own\u00a0 topographic\u00a0maps\u00a0with\u00a0QGis\u00a0.<\/p>\n\n\n\n

We will discuss here :<\/p>\n\n\n\n

– how to download elevation data for the area of interest<\/li>\n\n\n\n

– how to format the display style to fit the standards of the topographic maps<\/li>\n\n\n\n

– how to enhance the viewing using a \u201cshady\u201d layer type<\/li>\n\n\n\n

– and finally how to generate contours<\/li>\n\n\n\n

<\/li>\n<\/ul>\n\n\n\n
Download<\/strong> elevation<\/strong><\/h2>\n\n\n\nData<\/strong><\/h3>\n\n\n\nTo download the elevation data of your area of interest , go on page http:\/\/viewfinderpanoramas.org\/dem3.html<\/a><\/p>\n\n\n\n
This video  shows you the progress of the download .<\/p>\n\n\n\n
The data available  corresponds to a definition of 3 \u00a0\u00bb arc , about 75m. Every pixel of your DTM will display to this definition. In order for the DTM and the corresponding map to be  correct, you must work with an area of about a fifteen kilometers wide. For smaller areas, pixelation becomes visible and the quality of the topographic map fades.<\/p>\n\n\n\n
The downloaded tiles depict a size of 1 degree by 1 degree and are in a <\/em><\/strong> hgt <\/em><\/strong>format.<\/p>\n\n\n\n
This format is immediately readable by QGis . You can, therefore, load the tiles using adding raster in the Cartographic window.<\/p>\n\n\n\n
$\"\"$ <\/figure>\n\n\n\n
How toFormat<\/strong> the<\/strong> display<\/strong> style<\/strong><\/h3>\n\n\n\n
By default, the raster is displayed in shades of grey. Therefore it is necessary to apply some colouring adapted to accentuate the topography. Although it is possible to create your own color ramp or to use a color choice provided by QGIS, you can download by using the plugin   Color<\/em><\/strong> Ramp Manager<\/em><\/strong> .<\/p>\n\n\n\n
To install it, go in the menu   Extensions -> Install \/<\/em><\/strong> Manage Extensions,<\/em><\/strong> select the plugin   Color<\/em><\/strong> Ramp Manager<\/em><\/strong>   and click    Install<\/em><\/strong> the extension<\/em><\/strong> .<\/em><\/strong>  <\/em><\/strong> You will a new tool added to your tool bar :<\/p>\n\n\n\n
$\"\"$ <\/figure>\n\n\n\n
Click the tool to open the configuration window . Indeed, all the colour ramps are not installed automatically . The one that interests us specifically, cpt-city must be installed manually.<\/p>\n\n\n\n
\n
$\"\"$ Check the Full  box -City cpt package<\/li>\n\n\n\n
Choose the directory to install the package. Warning! by default this is the first option checked , but due to the fact that the Program Files directory is writing- protected , it will not work . You\u2019d rather choose QGis customization directory.<\/li>\n\n\n\n
Click on Check to start the update of the installation package.<\/li>\n<\/ol>\n\n\n\n
Once the package is downloaded, exit the dialog.<\/p>\n\n\n\n
Follow the video instructions to apply a colours ramp to your raster layer<\/p>\n\n\n\n
Add a Shady type layer \u201c(<\/strong> Hillshade)\u201d<\/strong><\/h3>\n\n\n\n
<\/em>To create this layer just go  to the Raster Menu-> Field Analysis -> Shading<\/p>\n\n\n\n
$\"\"$ <\/figure>\n\n\n\n
Give a name to this file to archive this new layer .<\/p>\n\n\n\n
However, it is essential to modify the Z factor. Indeed, the order assumes that you are working with a planar projection<\/a>, i.e. the XY coordinate of your raster layer are in meters. <\/span> $\"\"$ Since the layer is in decimals degrees  (latitude \/ longitude) you have to enter an appropriate conversion factor? The value to enter is 11120.<\/span><\/p>\n\n\n\n
Click OK to retrieve your new shading layer.<\/p>\n\n\n\n
$\"\"$ Now you only have to change the style of this layer to have a topographical image.<\/span><\/p>\n\n\n\n
Open the properties of the shading layer<\/p>\n\n\n\n
$\"\"$ <\/figure>\n\n\n\n
\n
Change the Min value to   125<\/em><\/strong>  <\/em> and the Max value to   255<\/em><\/strong><\/li>\n\n\n\n
Change the Merge Mode to   Multiply<\/em><\/strong><\/li>\n\n\n\n
Change the Brightness to   45<\/em><\/strong><\/li>\n\n\n\n
Change the Contrast to   20<\/em><\/strong><\/li>\n<\/ul>\n\n\n\n
The final result is as follows:<\/p>\n\n\n\n
$\"\"$ Create the contours <\/strong><\/p>\n\n\n\n
If you want to add contours, just go to the Raster menu -> Extraction -> Creating contours:<\/p>\n\n\n\n
$\"\"$ <\/figure>\n\n\n\n
\n
Give a location and a name to the new contours file<\/li>\n\n\n\n
Re-enter the interval, in meters, between the different contours<\/li>\n\n\n\n
Click Attribute Name if you want to have the elevation as an attribute for the field contours (if not, you will not be able to label the contours)<\/li>\n<\/ul>\n\n\n\n
$\"\"$ Once the order executed is , you will have the contours loaded :<\/p>\n\n\n\n
$\"\"$ <\/figure>\n","protected":false},"excerpt":{"rendered":"
Thanks to the SRTM project we can access to a comprehensive world coverage of land elevation data. It\u00a0has\u00a0become\u00a0very\u00a0simple to\u00a0create one\u2019s own\u00a0 topographic\u00a0maps\u00a0with\u00a0QGis\u00a0. We will discuss here : Download elevation Data To download the elevation data of your area of interest , go on page http:\/\/viewfinderpanoramas.org\/dem3.html This video  shows you the progress of the download . The data available  corresponds…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"give_campaign_id":0,"_bbp_topic_count":0,"_bbp_reply_count":0,"_bbp_total_topic_count":0,"_bbp_total_reply_count":0,"_bbp_voice_count":0,"_bbp_anonymous_reply_count":0,"_bbp_topic_count_hidden":0,"_bbp_reply_count_hidden":0,"_bbp_forum_subforum_count":0,"sfsi_plus_gutenberg_text_before_share":"","sfsi_plus_gutenberg_show_text_before_share":"","sfsi_plus_gutenberg_icon_type":"","sfsi_plus_gutenberg_icon_alignemt":"","sfsi_plus_gutenburg_max_per_row":"","_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_post_was_ever_published":false},"categories":[1260],"tags":[],"class_list":["post-5000","post","type-post","status-publish","format-standard","hentry","category-non-classe-en"],"aioseo_notices":[],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/p6XU0A-1iE","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.sigterritoires.fr\/index.php\/wp-json\/wp\/v2\/posts\/5000","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.sigterritoires.fr\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.sigterritoires.fr\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.sigterritoires.fr\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.sigterritoires.fr\/index.php\/wp-json\/wp\/v2\/comments?post=5000"}],"version-history":[{"count":0,"href":"https:\/\/www.sigterritoires.fr\/index.php\/wp-json\/wp\/v2\/posts\/5000\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.sigterritoires.fr\/index.php\/wp-json\/wp\/v2\/media?parent=5000"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.sigterritoires.fr\/index.php\/wp-json\/wp\/v2\/categories?post=5000"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.sigterritoires.fr\/index.php\/wp-json\/wp\/v2\/tags?post=5000"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}