Basemap

PREPARING A BASE MAP
Before you can create an orienteering map, you need some type of map to use as a foundation or pattern. This is called a base map. Your base map should be accurate enough to provide exact locations of large point features, such as roads, rivers, lakes, and major terrain features, so you can accurately place the details you collect during the field checking process.

Collecting Existing Maps
Gather all you can find on the area; topo maps, aerial photographs, park maps, old orienteering maps, engineering maps, landscape drawings or site plans. Most states have a Department of Natural Resources that may have useful map data. Many county governments are putting their tax assessor's office online with property boundaries and recent aerial photographs. Be sure the maps are geographically accurate and not merely artistic diagrams of the park.

Select a Common Scale
Orienteering maps are typically 1:10,000 or 1:15,000, however other scales may be used for special projects like Park-O or Bike-O. Whatever scale you choose, you'll need to convert the maps you've collected to that scale so that distances and size scan be accurately measured.  The height-to-width ratio all the images should be about 1.3, which is the same as a letter-sized page. A good program for manipulating image files is IRFANview.

Sources
Here are some sources of map data along with some recommendations:

The National Map
 - topographic maps (DRG)
 - aerial photos (DOQ)

 County Gov (tax assessor)
 - aerial photos
 - property boundaries (cadastral maps)
 - engineering maps

 Google maps
- aerial photos

Open Street Map
 - streets, rivers, trails, buildings, lakes, power lines


 Go to the OpenStreetMap.org website. Browse to the area of interest and zoom in to the area you would like to map. At the top of the screen you will see an "Export" button. This function allows you to save the map as an OSM file. The OSM file can be opened by the Open Orienteering Mapper (OOM) program and converted to an orienteering map symbols. This basic map will include roads, streets, park outlines, and some trails and water features. The scale will be set so that distances can be measured correctly, but much of the details will be left for the mapper to add.

 OSM data varies greatly from location to location. Some areas will have only paved roads and major rivers; others areas have building outlines and hiking trails mapped correctly. OSM is a volunteer-driven project that depends on local enthusiasts to contribute data. Once the map is create in OOM, you can start adding details like ditches, boulders, open fields, and hiking trails.

 Here are some instructional videos by Michael Eglinski of Orienteer Kansas:

Download map data from Open Street Map
https://www.youtube.com/watch?v=aHX3kazeJVI
Base maps for a small orienteering map from openstreetmap.org and nationalmap.gov

Start a new map in Open Orienteering Mapper from a OSM data file:
https://www.youtube.com/watch?v=2iTWRm0D62o
Using Open Orienteering Mapper(OOM) to create a base map and national map data

 The OOMapper program also has the ability to import data from a GPS receiver. Walk all the trails with your GPS and save the track as a GPX file. This GPS track file can be converted to the symbol for trails, vehicle track, or footpath.

 Orienteering maps are oriented to magnetic north, but aerial photos and GPS data use true North. At some point the map should be rotated to put magnetic north at the top of the map.

The difference between true north and magnetic north is called declination. Declination changes gradually from year to year, and is different for each location. The National Geophysical Data Center monitors and maps changes in the declination. You can look up the declination at your location here:
 https://ngdc.noaa.gov/geomag/geomag.shtml

 Draw as much of the map as you can by using aerial photographs and GPS data before rotating the map. After this rotation, you can easily use a compass for more detailed fieldwork. This rotation should be done only once, and you should have a backup copy of the map before you attempt rotation. The author's experience with rotating back to true north was not a good one.

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