Spikes, the bane of elevation mappers every where, well not any more.
One cause of spikes is due to elevation maps having a "no data" pixel used for areas like the ocean.
If your coast line has spikes this is the cause, but luckily its easy enough to fix.
As a elevation mapper you will need to download and install QGIS, a free and totally great tool for us, so get it.
One you have done that, Open your elevation file into QGIS and select it.
To fix the "no data" pixels we have to identify which value your map uses, so double click your layer to bring up its properties.
Under "Bands" you will find your "No data value"
In this case the no data value is -9999, we need to remember this for later.
Now we have to tell the game that pixels with a value -9999 is no data represented as 0/0.
Click on the following Menu's: SAGA then "Processing" and then "tool box"
Next select "Raster Tools" and then "Reclassify Values (Simple)" Click on the button with the three dots for "Lookup Table"
Click "Add Row"
Enter the No Data value form earlier, which in our case was -9999 and well will replace this with 0/0 no data as shown below.
Click OK and then click run.
Next export this new layer as normal. And geoconvert without spikes caused by no data pixels. Enjoy
Spikes due to Pixel data type use the Raster > Conversion > Translate tool.
This guide is intended for users who have at the least read ans understood the elevation guides by Qwerty42 and Crispy136.