![]() The choice of projection depends on a map’s use, scale and audience. The only exception is a Globe, which preserves angles, areas and distances perfectly. Projection almost always introduces distortion, most projections cannot preserve angles, areas and distances at the same time, they may be conformal (angle-preserving), equal-area (area-preserving) or equidistant (distance preserving) but not all at once. The task of projecting, or unfolding the spherical Earth onto a flat map, is an age old problem in cartography. Tagged Labels, Map, QGIS, Tutorial Creating a Tissot’s Indicatrix in QGIS #Symbols quantum gis trialSome trial and error is may be required to find the correct label position. “ Angle” and (“Angle”) * -1, or a value other than 90° depending on the symbol used and the prefered label placement location. You may need to use a different expression e.g. Lastly, the expressions “Angle” – 90 and (“Angle” – 90) * -1 were necessary in my case because I needed to place my labels next to the dip and strike symbol’s barb. It took me a few tries before I found the right distances for my geological symbols, from 90 to 230 meters distance depending on the symbol size and type. You may have several different symbols, of various sizes, each requiring an appropriate label distance expressed in the Attribute Table. #Symbols quantum gis licenseGeological Survey of Ireland – Creative Commons Attribution 4.0 license We see that the dip labels rotate and currently follow the orientation of the dip and strike symbols (note that the points are at the intersection of the T symbol). The following geological map of the Old Head of Kinsale in southern Ireland shows the results of the above procedure. ![]() Enter the following expression in the Data Defined Override dialogue: Layer Properties – Labels – Placement – Data Defined – RotationĬlick the Data Defined Override Icon again and then choose Edit. Then enter the following expression in the Data Defined Override dialogue:įinally, to control the rotation of label text, so text follows the orientation (angle) of a rotating symbol or icon, choose: Layer Properties – Style – click Data Defined Override icon – Edit You may also optionally control the angle of a symbol or icon itself via: The expression takes the angle and distance values from the Attribute Table (edited earlier) and calculates an X, Y label position relative to the point feature. Enter the following expression in the Expression String Builder window: Right click the points layer and choose:Ĭheck that Offset From Point is checked and then click the Data Defined Override next to the Offset X, Y boxes and choose Edit. The Expression String Builder will appear. ![]() The next step is to control the position of the label around the points using trigonometry. Note – I use Strike (Angle) and Label Distance (Distance) in my Attribute Table Also, I chose Map Units (not millimeters) for Symbol Size, Font Size and Distance for my map, as I prefered to keep symbol size, font size and position of labels fixed when zooming in and out. You can add Angle and Distance values to these columns manually or use the Field Calculator (see below) to add values if you have lots of points.
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