Scalebar Trouble

[Andy C]

Hello there,

I am having a bit of trouble producing an accurate scalebar on a map I'm trying to create, and was wondering whether I could trouble anyone to offer a hand.

It's a rather simple map with only two data layers (a basemap of the UK, and a layer displaying observation locations) and I have confirmed that both of those layers, as well as the project itself, are all using the same CRS (OSGB 1936 / British National Grid - EPSG:27700, and I also used this for the map grid which seems to be fine).

Prior to producing the map, all I had done was to download a UK basemap file and add it as a layer, and then produce the observations layer from a .txt file containing latitude and longitude data.

I am still using QGIS 2.8.3, and have adapted the instructions from the textbook GIS For Biologists - A Practical Introduction for Undergraduates, to get to where I am, which I have done without hitch other than for this issue. Interestingly the only scalebar units available to select are 'Map Units', 'Meters', 'Feet' and 'Nautical Miles'.

I don't know whether they will help at all but I've attached a couple of screenshots.

Many thanks,

Andy.

[Andy C]

Hello,

Further to the above, I am using Windows 10 and downloaded the basemap from Diva-GIS (www.diva-gis.org/gdata).

Thanks again,

Andy.

[cdma...@gisinecology.com]

Hi Andy,

It looks like there has been a problem with the transformation of your data layers into the Britih National Grid projection. This means that all your features are very small, and this explains why the scale part is showing such a short distance (4 metres).

The problem with the projection transformaiton is almost certainly because you have changed the projection in the LAYER PROPERTIES window from WGS 84 to British National Grid,. If you do this, it does not do the tansformation properly and you end up with very small features that don't plot in the rigth place.

The way to solve this is to go back into the LAYER PROPERTIES window for each data layer and re-set them to WGS 84. Don't worry if they appear to disappear, just right click on their name in the TABLE OF CONTENTS window and select ZOOM TO LAYER window and they will re-appear.

Next, right click on the name of the first data layer and select SAVE AS. This will open the SAVE AS window. In this window, you can set he new projection you wish to transform the data layer into in the CRS section. Once you have done this, save it with an appropriate name and in an appropriate location on your computer.

Do this for the other data layers.

Once you have done this, you will need to build yourself a new map in a new PRINT COMPOSER window. When you do this, your scalebar should now look much better and have the right units on it.

If this doesn't work, just reply to this thread.

All the best,

Colin

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