Starting a new project based on an old map
Imagine that you wanted to start making a new orienteering map, and wanted to use an old map or image as a basis. Here’s one way to achieve that.
We’ll use Open Orienteering Mapper for the project, and some reference points from Open Street Map.
The process we’ll be following is:
- Starting a new project
- Getting reference data and loading it as map templates
- Loading an old map as a template
- Adjusting the old map template to align with the new project’s co-ordinate system.
The result will be a geo-referenced template, ready to serve as the background image for a new orienteering map. You can draw your new map on top of it, using the template as a guide.
Start a new map in Open Orienteering Mapper
We’ll create a brand new map for this project.
Start the geo-referencing process for the blank map.
Our map will be in UTM area 55 S (see Understand the co-ordinate system). It will be centered at the latitude and longitude of 35.3081804 S, 149.1244213 E. This area has a magnetic declination of 12.3 degrees (the difference between true north and the magnetic north).
The result isn’t much to look at. In fact, it looks like we’ve achieved nothing at all. But now we’re ready for the next step.
Estimate the scale of the old map
Let’s use this digitised old plan for the Canberra area, by Walter Burley Griffin in 1916, as our base image. We could have used an aerial photograph or an old orienteering map instead of this old map. The process is the same for all non-geo-referenced images.
To figure out the scale of the old map, we can examine its own scale in an image editor (I’m using Windows Paint). Place the cursor at the zero mark of the scale, and note the image pixel co-ordinates. Our zero mark is 1140 horizontal pixels into the image.
At the other end of the scale, 6000 feet, the cursor is 1717 horizontal pixels into the image.
The WolframAlpha website shows us that the scale can be expressed as 3.169 metres per pixel.
Find some reference points on the old map
There are a few places on the old map that have known latitude and longitude. We’ll use those to transform the template in Open Orienteering Mapper.
The old map has a point showing the peak of Black Mountain. We’ll use that for geo-referencing later. We’ll also use the peaks of Mount Ainslie and Capital Hill. Any recognisable points would have served our purpose.
Get latitude and longitude for the reference points
Open Street Map can be a very convenient way to get the latitude and longitude of the reference points. In the image below, I’ve selected the peak of Black Mountain, noted the latitude and longitude, and downloaded an XML file with the details.
To make it easier to see the reference point later in Open Orienteering Mapper, I’ll export some of the surrounding area too.
I’ll also do the same some for the other reference points.
Loading the reference data into Open Orienteering Mapper
In Open Orienteering Mapper use the Template setup window (menu: Templates / Template setup window) to load the reference points and areas. My three reference points and their surrounding areas have been loaded in the image below.
Load the old map template
Now it is time to load the old map as a template. Use the scale that was calculated earlier. It isn’t essential to get it right, since it will be adjusted later anyway.
The result is that we now have all the reference points and the old map loaded into Open Orienteering Mapper.
The old map isn’t aligned with the reference points yet.
Transforming the old map
The old map may need to be scaled, moved and rotated before it is useful to us. The Open Orienteering Mapper template adjustment process will take care of the details. Our main job is to find pairs of points (“pass points”), one on the old map template and one on the new map coordinate system, for Open Orienteering Mapper to use. Two pairs are needed, as a minimum. I’ll use three pairs of pass points in this example.
Start the process by organising the screen so that you can see the reference point in the old map and the Open Street Map templates. Zoom and adjust the transparency of the template layers as required.
In the example below, you can see the Black Mountain peak on the old map, its corresponding Open Street Map point and the Open Orienteering Mapper button to start the adjustment process.
Create the first pair of pass points by starting the adjust process, using the New button (#1 in the image below), clicking on the old map’s reference point (#2), clicking on the reference point (#3), and observing the result (#4).
Repeat the process for the other reference points. The image below shows my three pairs of pass points (with red connecting lines). Set the ‘Apply pass points’ box to execute the adjustment.
The result is that the old map template is scaled, moved and rotated so that the pairs of points are aligned.
Next steps
Our old map is now ready to serve as the basis of our new geo-referenced project.
Hide or remove the unwanted reference templates, and proceed with your project.
Alternatives
There are lots of other workflows that you could use instead of the method described here. You are welcome to share your ideas in the comments.
About
This article is part of the Orienteering Mapping with LiDAR, Smartphones and Free Tools series. All these articles are placed into the public domain. You can use the articles as you please. There’s no need for attribution.
Polite and constructive responses are always welcome.
