{"id":2176,"date":"2018-09-07T10:49:21","date_gmt":"2018-09-06T22:49:21","guid":{"rendered":"http:\/\/blogs.lincoln.ac.nz\/gis\/?p=2176"},"modified":"2023-05-07T03:29:36","modified_gmt":"2023-05-07T03:29:36","slug":"save-your-marriage-use-layer-files","status":"publish","type":"post","link":"https:\/\/blogs.lincoln.ac.nz\/gis\/save-your-marriage-use-layer-files\/","title":{"rendered":"Save your marriage – use layer files"},"content":{"rendered":"

Layer files are a useful way to recreate legends and get consistent symbology.\u00a0 This post outlines what they are and how to use them.\u00a0 <\/em><\/p>\n

Geology…who doesn’t love geology?\u00a0 And who doesn’t love geology maps especially?\u00a0 (Ed. – Only heathens…<\/em>)\u00a0 The image below shows one of the\u00a0 1:250,000 scale geology maps that cover the country, produced by Geological and Nuclear Sciences<\/a> (GNS).\u00a0 They are rich in detail and symbology and anyone who uses them frequently will be familiar with the shadings, and colours and patterns that describe our geology underfoot.\u00a0 Here’s an image of the whole map but we’ll only focus on a few aspects:<\/p>\n

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Here’s an image zoomed in on the Christchurch\/Banks Peninsula area:<\/p>\n

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And here’s a portion of the legend – it’s quite an extensive, custom legend and I can only show a small part to give you the sense of detail but I hope you get the picture:<\/p>\n

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If I’d like to recreate the look and feel of these data on my own map, I’ll first need the same data.\u00a0 Happily, we have copies of all the data layers that make up these maps – you can find them in J:\\Data\\QMAP-250K.\u00a0 The main layer of interest is probably the “NZL_GNS_250K_geological_units” feature class, which I’ll show you on the map below (using ArcGIS Pro<\/a>):<\/p>\n

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By default, any new layer added is shown as a single symbol for all features, so there’s not much to differentiate one unit from another.\u00a0 Amongst the many attributes is one called “plotName” which is what is usually shown on the maps.\u00a0 So I’ll change the symbology to Unique Values and let it assign a colour to each unit and zoom in, as shown below:<\/p>\n

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Hmmmm…the same data, yes, but how do I get it to look like the standard geology map from GNS?\u00a0 I’ve got two options.\u00a0 I could go through each symbol, unit by unit and try to match each as best I can.\u00a0 This is painstaking business and fraught with frustration.\u00a0 LOTS of frustration.\u00a0 Something like this could end a marriage.\u00a0 Or make someone quit and join an ashram in southern India.\u00a0 Option two is a lot more feasible.<\/p>\n

Layer Files<\/strong><\/p>\n

The good people at GNS went to great lengths to symbolise their maps.\u00a0 So much so that they have made that symbology transportable in the from of layer files<\/a>.\u00a0 We’ve talked about these once before<\/a> in a different context.\u00a0 Layer files are sort of front ends\u00a0on data layers that have captured the symbology choices.\u00a0 If you look in the QMAP-250K > Support > Layerfiles folder you’ll see there\u00a0is another folder called\u00a0NZL_GNS_250K_geology (2nd edition).\u00a0 Inside that<\/em> (have you left a trail of breadcrumbs?) is a collection of files, all ending in .lyr and with names that match the feature class layer names.<\/p>\n

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These layer files will make it a lot easier to get our symbology to match GNS’s – because it\u00a0tells Pro (or ArcMap) how to render the data.\u00a0 Note the file sizes – these layers contain no spatial data.\u00a0 Think of them as the saved legend for each of the layers shown on the GNS map.\u00a0 Happily we can import these layer files and use them for our symbology.\u00a0 Here’s how:<\/p>\n