[ home ]

Make a scale diagram from a satellite image

• Download a PDF file with a 1:1000 scale plan and satellite image of Birmingham Town Hall
• I used Google Maps with the postcode
• I've made similar scale plans of the locations where I teach numeracy
• You can resize the screengrabs of the satellite photos and plans in OpenOffice Writer or Word so that the scales are 'easy' numbers

Google Maps and the satellite view make it easy to generate images of the buildings where you teach or other local landmarks. Use the Google Maps 'zoom' feature to frame a place or feature that will interest the students. I've used large area maps showing several Km of a locality leading to scales like 1:30 000, and I've used small area satellite photos leading to scales as small as 1:500. You can screen grab these images, then crop them in a paint program and save the file as a jpg or png file. When cropping the file, make sure you include the scale bar in the bottom left corner.

To make a screen grab in Windows, just arrange the browser window how you want it, and then

• Press and hold the ALT key on the left of the space bar
• Press the Print Screen key (labelled PrtScr or SysRq)
• A copy of the current window is made in the clipboard
• You can paste the picture into Paint or another image editing program
• Crop and save as a jpg or png file
• On laptops, you may need to press the Fn key to access the PrtScr or SysRq key as the manufacturers double up some of the less common keys to reduce the size of the keyboard

In Linux, there is usually a screenshot program included with the desktop, or use the screen shot facility built into Gnu Image Manipulation Program

Then you can 'insert' the image into a wordprocessor. In MS Word and OpenOffice

• Click Insert | Picture | From File.
• Position the image in a way that suits your handout
• Print one copy
• Measure the length of the scale bar - in my town hall satellite image, the 20m bar measured 22.5mm in length
• Calculate an appropriate factor to resize the image to to make the scale factor an 'easy' number
• In my example, I calculated 20m divided by 22.5 resulting in 0.888...

Now switch back to the image in the wordprocessor file and

• Right click over the picture
• Bring up the Image or Picture menu item
• Select the Resize tab (MS Word) or look for the Type tab in OpenOffice
• Make sure that the Keep Ratio box is ticked
• Read the width of the image in cm or %
• Multiply the width by the fraction you calculated above and then set the width box to the new width
• Click OK
• The image will resize slighty

You now have an image or plan scaled to an 'easy' number like 1:500 or 1:1000 or 1:30 000

As you can see the Town Hall satellite photo shows a range of shapes and features that can be measured. The Google 'tilt' or perspective effect on the satellite images can provide for discussion around 3-d representation. The 'reality' of the satellite photo also requires students to decide how to measure features. We have estimated the area of lakes using the trapezium method in higher level classes.

Keith Burnett, Last update: Sun Sep 04 2011