update links

Author: jmckenna

en/mapfile/symbology/construction.txt

@@ -33,7 +33,7 @@ dissertation will also concern this subject.
 
 The document has been heavily revised for MapServer  6.
 
-.. _`Download study report`: http://www.mapmedia.de/fileadmin/user_upload/dokumente/umn_signaturen_howto/Praktikumsarbeit.zip
+.. _`Download study report`: https://download.osgeo.org/mapserver/docs/Praktikumsarbeit-2004.pdf
 
 
 Introduction
@@ -2233,7 +2233,7 @@ note, that your MapServer must at least be able to handle 50
 symbols. Otherwise you will get an error while loading the *symbol*
 files.
 
-.. _`download_old_symbols`: http://www.mapmedia.de/fileadmin/user_upload/dokumente/umn_signaturen_howto/vortrag_demo.zip
+.. _`download_old_symbols`: https://download.osgeo.org/mapserver/docs/vortrag_demo.zip
 
 
 Basic Symbols
@@ -2594,4 +2594,4 @@ You can also view the
 `discussion paper for the improvement of the MapServer Graphic-Kernel`_
 (German only).
 
-.. _`Discussion paper for the improvement of the MapServer Graphic-Kernel`: http://www.mapmedia.de/fileadmin/user_upload/dokumente/umn_signaturen_howto/DiskussionsPaper-UMNGraphikKernel.pdf
+.. _`Discussion paper for the improvement of the MapServer Graphic-Kernel`: https://download.osgeo.org/mapserver/docs/DiskussionsPaper-UMNGraphikKernel.pdf