Using Scale
Google Maps
Google Maps is a great tool to calculate the distance between two points anywhere in the world.
Click on ‘Maps Labs’ on the bottom left corner of your screen and make sure the Distance Measurement Tool is enabled.
You can now find the exact distance between two points by clicking on the ruler icon on the bottom left corner of the map.
Google Maps Distance Measuring Tool, Auckland to Sydney (Source: maps.google.com)
How big is it?
Scale is the ratio of a distance on a map or photo to the equivalent distance in real life. Every photo and map you’ll ever see uses a scale because obviously a photo of something, especially something huge like the Harbour Bridge, can’t always be as big as the object itself. Scales are expressed as a ratio such as 1:1000, where 1cm on the map is the equivalent of 1000cm in real life.
The scale should be consistent for both the width and height of the photo. If it isn’t, the photo will look out of proportion. Look at the photos below. Which one uses a more consistent scale?
Sydney Opera House (Source: en.wikipedia.org)
Calculating Scale
We can calculate the scale a photograph or map is using by looking at features or landmarks that have standard dimensions. Take a look at this photo. What size is an Olympic swimming pool? Can you calculate the scale of the photo?
Swimming pool scale (Source: http://taxdollars.blog.ocregister.com/)
We know that an Olympic swimming pool is 50m long. In the photo, the same size pool is only 50cm. Therefore the photo is using a scale of 50cm:50m, which can also be expressed as 50cm:5000cm. Simplifying this, we can say the photo is using a scale of 1:1000
Calculating Distances
Using the same process in reverse, we can calculate distances on a photo or map if we know the scale. Have a look at the site plan below and try and answer the following questions:
- What is the scale of the site map?
- Using the scale, what is the length of the site along Yawalpah Road?
- If the site is a perfect square, what is its perimeter?
- What is the area of the site?
Scaled Site Plan (Source: http://www.arcadiawoods.com.au/media/siteplan-large.jpg)
We know the scale of the photo is 1:10000. If the length of the site is 20cm on the map, then its actual length is 20cm x 1000. Therefore its length is 200,000cm or 2km.
If the site is a square then all its sides are of equal length and must be 2km. Four sides that are each 2km in length means the site has a perimeter of 8km.
To calculate area, we must multiply the length by the width (A = L x W). Multiplying 2km by 2km, we find the area of the site to be 4km2.