3 Area

How big ...

How to calculate

... if irregular shape?

Area of the rectangle?

... convert to regular shape(s)

L x W

how big is the bat?

Area of the rectangle if

it is a 1: 10,000 map?

b/c the boxes & triangles are all different sizes, this can take awhile

Area

Steps for Strips (Lined Paper):

1) line spacing (width)

• measure across several (10?)

Why? To improve the answer. There can be quite a difference in printing quality and line spacing consistency. If you measure across 10 (and then obviously divide by 10) you overcome this.

2) total all the strips (length)

this speeds things up as the strips have a uniform width

3) convert to RW measures (m)

size of a 2D shape (polygon)

expressed in sq. units

• cm2 ... m2 ... acre, ha (= 10,000 m2)

4) Area (m2) = L (m) * W (m)

m2 / 10,000 = ha

error/ uncertainty?

tools

graph paper or dot grid

each step:

- grid size (line spacing)

- conversion to RW units

- tally of dots (length of lines)

Count 2: Intersections

• 25 fully in
• 4 borderline
• = 25 + (1/2 * 4)
• = 27 squares

Count 1: Squares

• 16 full
• 20 part
• = 16 + (1/2 * 20)
• = 26 squares

planimeters

Ave count = 26.5

Google Maps - Area Calculator

• right-click, measure distance
• area given once closed

https://www.google.ca/maps/@49.1624169,-123.9556994,14z

1.05cm

??

1

5,000

Steps for Dot Grid (Graph Paper):

1) measure grid spacing (across many)

2) convert to RW units (metres)

GRID SIZE

fine - counting difficult

coarse - variable count

solution

• moderate grid size
• ave 2 counts

(1.05 cm * 5,000)/1

? = 5,250 cm

? = 52.5 m

3) calc. area (m2) of 1 dot (square)

• divide by 10,000 = ha per dot

dot count = 23 full + (1/2 * 3 half)

= 24.5 dots

area = 2,756 m /dot * 24.5 dots

= 67,522 m

= 6.8 ha

4) tally the dots (borderline dots?)

5) Area (ha) = dot count * ha / dot

which is more accurate ...

... dot (graph) OR line ?

so 1 dot = 1.05 cm