{"id":204,"date":"2015-05-18T13:42:02","date_gmt":"2015-05-18T13:42:02","guid":{"rendered":"http:\/\/transnationalhistory.net\/mapping\/?page_id=204"},"modified":"2023-08-29T15:13:38","modified_gmt":"2023-08-29T15:13:38","slug":"advanced","status":"publish","type":"page","link":"https:\/\/transnationalhistory.net\/mapping\/tutorials\/baselayer\/advanced\/","title":{"rendered":"One Step Further: Smoother Coastlines & Raster Layers"},"content":{"rendered":"

ONE STEP FURTHER #1: Smoother Coastlines<\/strong><\/span><\/p>\n

As you saw in the first tutorial, some areas of the coastline may look a little bit messy, due to the geographic complexity of the region. That is the case, for instance, of the south of Chile or the fjords of Norway. There is a way to simplify the coastlines.<\/p>\n

Let’s take the example of Northern Europe, including Norway and its numerous fjords.<\/p>\n

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In order to obtain a simplified rendition of the western coast, let’s open the Simplify Geometries<\/strong> tool that you can find under\u00a0Vector<\/strong> then\u00a0Geometry Tools<\/strong>.<\/p>\n

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A new window then opens. Make sure you are selecting the right layer to modify. You may want to tick the\u00a0Save to new file<\/strong>\u00a0box or you might lose the original layer.<\/p>\n

The most important option is the\u00a0Simplify tolerance<\/strong> scale. This depends on the scale your map will be at. If you want to work exclusively on Norway, but you think there is still too much detail, you may want to choose a very mild scale (0.01 for instance). If you are working globally and you only want to get rid of the ‘messy’ aspects of certain parts of the world, opt for a bigger ratio (0.1). Please note that anything above 0.5 will have a very significant impact on your map.<\/p>\n

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I have opted for 0.1. After clicking\u00a0OK<\/strong> the result is deplayed along side many red dots.<\/p>\n

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\"\"These are the angles of the layer that you can keep editing (we will see this in a later tutorial<\/a>). Click on the\u00a0Toggle editing<\/strong> button if done, and confirm that you wish to save the layer.<\/p>\n

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\nThis option simplifies your layer: it reduces the number of lines, and therefore the result may not be satisfactory to you, as it looks too rough and not round enough. You can use a second option (either combine it with the first one or use it on its own) called the Generalizer<\/strong>.<\/p>\n

\"1<\/a>Before being able to use it, you need to install the plugin into QGIS. To do so, go to\u00a0Plugins<\/strong> and\u00a0Manage and Install Plugins<\/strong>. Search for\u00a0Generalizer<\/strong> and make sure the box is ticked and the plugin installed. Then click again on\u00a0Plugins<\/strong> and choose\u00a0Generalizer<\/strong>.<\/p>\n

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The Generalizer is composed of many algorithms which will all be very useful to complete a certain task. Remove small objects<\/strong>, for instance, will get rid of tiny islands so your map looks tidier.\u00a0No matter what algorithm you are choosing, make sure you select the right layer<\/strong>. Once you click OK<\/strong>, a new window will ask for a CRS. Pick the same as your original layer, most commonly WGS 84<\/strong>.<\/p>\n

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There are several algorithms available to make coastlines look smoother. I am choosing Chaiken’s Algorithm, which is pretty easy to use as it is separated in levels.<\/p>\n

Here are the results with Level 1, Weight 3.00 <\/strong>combined with the previously simplified map.<\/p>\n

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If I’m starting from the original coastline layer (without simplifying), this algorithm is not very effective. I am opting for another algorithm (Boyle’s Forward-Looking Algorithm, look-ahead 10).<\/p>\n

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Three tips: <\/strong><\/p>\n