GGH2603
Notes
Exam Prep
Assignmen
t Prep
, Understanding image scale and resolution
The terms "scale" and "resolution" are often used in remote sensing discussions,
and it is important to know what they mean and how they differ. They both
influence the detail that can be seen on an image but beyond that they are quite
different.
Scale
The image scale or map scale as it is sometime called refers to the relative
difference in size or distance between the image and the features represented
on the ground. This difference is written as a ratio of image distance over ground
distance. For example, a scale of 1:100,000(one to one hundred thousand)
means 1 centimeter on the map equals 100,000 centimeters(1km) on the
ground. The following is a list of scales and equivalent ground distances for three
distances measured on an image.
Image scale 1 mm on image 3 mm on image 5 mm on image
1:10,000 10 m 30 m 500 m
1:40,000 40 m 120 m 2,000 m
1:100,000 100 m 300 m 5,000 m
1:500,000 500 m 1,500 m 25,000 m
A similar table can be made for areas where the area on the ground (in hectares)
is given for three square areas measured on an image.
Image scale 1 mm X 1 mm 3 mm X 3 mm 5 mm X 5 mm
1:10,000 0.01 ha 0.09 ha 25 ha
1:40,000 0.16 ha 1.44 ha 400 ha
1:100,000 1.00 ha 9.00 ha 2,500 ha
1:500,000 25.00 ha 225.00 ha 62,500 ha
One often refers to a scale as being larger or smaller than another scale. This
can be confusing, especially since scales are often referred to solely by their
denominator.
For example a scale of 1:100,000 (one to one hundred thousand) may be called
a scale of 100,000 when it is actually a ratio of 1/100,000. A scale of 1:100,000 is
smaller than a scale of 1:40,000 because the number 1/100,000 is smaller than
1/40,000 (or as it is often stated, a scale of 100,000 is smaller than a scale of
40,000). Another way to look at this is to think of a lake on an image with a scale
of 1:100,000 and another with a scale of 1:40,000.
The lake will be larger on the 1:40,000 image because the scale is larger. One
way to avoid the confusion between large and small scale is to use the terms
“coarse scale” and “fine scale”.
Notes
Exam Prep
Assignmen
t Prep
, Understanding image scale and resolution
The terms "scale" and "resolution" are often used in remote sensing discussions,
and it is important to know what they mean and how they differ. They both
influence the detail that can be seen on an image but beyond that they are quite
different.
Scale
The image scale or map scale as it is sometime called refers to the relative
difference in size or distance between the image and the features represented
on the ground. This difference is written as a ratio of image distance over ground
distance. For example, a scale of 1:100,000(one to one hundred thousand)
means 1 centimeter on the map equals 100,000 centimeters(1km) on the
ground. The following is a list of scales and equivalent ground distances for three
distances measured on an image.
Image scale 1 mm on image 3 mm on image 5 mm on image
1:10,000 10 m 30 m 500 m
1:40,000 40 m 120 m 2,000 m
1:100,000 100 m 300 m 5,000 m
1:500,000 500 m 1,500 m 25,000 m
A similar table can be made for areas where the area on the ground (in hectares)
is given for three square areas measured on an image.
Image scale 1 mm X 1 mm 3 mm X 3 mm 5 mm X 5 mm
1:10,000 0.01 ha 0.09 ha 25 ha
1:40,000 0.16 ha 1.44 ha 400 ha
1:100,000 1.00 ha 9.00 ha 2,500 ha
1:500,000 25.00 ha 225.00 ha 62,500 ha
One often refers to a scale as being larger or smaller than another scale. This
can be confusing, especially since scales are often referred to solely by their
denominator.
For example a scale of 1:100,000 (one to one hundred thousand) may be called
a scale of 100,000 when it is actually a ratio of 1/100,000. A scale of 1:100,000 is
smaller than a scale of 1:40,000 because the number 1/100,000 is smaller than
1/40,000 (or as it is often stated, a scale of 100,000 is smaller than a scale of
40,000). Another way to look at this is to think of a lake on an image with a scale
of 1:100,000 and another with a scale of 1:40,000.
The lake will be larger on the 1:40,000 image because the scale is larger. One
way to avoid the confusion between large and small scale is to use the terms
“coarse scale” and “fine scale”.
