contours of the world available from the NASA shuttle mission.
http://dds.cr.usgs.gov/srtm/version2_1/Documentation/SRTM_Topo.pdf
http://dds.cr.usgs.gov/srtm/version2_1/SRTM30/srtm30_documentation.pdf
See also DEM data at http://www.viewfinderpanoramas.org/Coverage%20map%20viewfinderpanoramas_org3.htm
http://www.terrainmap.com/rm39.html
A high quality DEM from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument of the Terra satellite is also freely available for 99% of the globe, and represents elevation at 30 meter resolution. A similarly high resolution was previously only available for the United States territory under the Shuttle Radar Topography Mission (SRTM) data, while most of the rest of the planet was only covered in a 3 arc-second resolution (around 90 meters).
https://tandemx-science.dlr.de/ high res earth mapping
or use OS :
http://www.ukmapcentre.com/acatalog/height-data-contours-dtm.html?gclid=COHrwtvRvcECFRMatAodRkQALQ
https://www.ordnancesurvey.co.uk/opendatadownload/products.html
to convert os data to sketchup:
http://www.geoplanit.co.uk/?p=103
online mapping :
http://www.openstreetmap.org/#map=14/57.7987/-5.2579&layers=C (roughish 10m contours from opencyclemap)
http://www.arcgis.com/home/webmap/viewer.html?useExisting=1&layers=30e5fe3149c34df1ba922e6f5bbf808f (smooth 25m contours)
http://www.esriuk.com/software/arcgis/free-mapping-software
http://www.qgis.org/en/site/ http://www.kyngchaos.com/software/qgis