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Pie Graphing in Geography

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Pie Graphs are used when all of the things you are working with can be placed into separate categories. Pie Graphs are useful to compare. General Rules 1)Everything you have can be placed into a group / category. 2)No one thing fits into more than one group.

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Pie Graphs Use 360 degrees of a Circle to represent 100% I nteresting point … 360 divided by 100 = 3.6 ¼ of a pie = 25% ¾ = 75%

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Once you have chosen DATA to PIE Graph ….. Step 1 – Build a RAW Table of DATA This table will have 4 columns Some Rounding rules - round percent numbers to one decimal place - round degrees to the nearest whole number example: class eye colour Raw Data Category number Blue 8 Green 12 Hazel 6 Brown 4 TOTAL 30

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This class of 30 has 4 different Eye colours Next … add a column for percentage and DO THE MATH

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Category number Percent Blue 8 (8/30)*100 = 26.7 Green 12 (12/30)*100 = 40.0 Hazel 6 (6/30)*100 = 20.0 Brown 4 (4/30)*100 = 13.3 TOTAL 30 100.0

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Add the fourth column - here you calculate degrees from the percent numbers In this column take the percentage and multiply by 3.6

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Category number Percent Degrees Blue 8 (8/30)*100 = 26.7 26.7*3.6= 96 Green 12 (12/30)*100 = 40.0 40.0*3.6= 144 Hazel 6 (6/30)*100 = 20.0 20.0*3.6= 72 Brown 4 (4/30)*100 = 13.3 13.3*3.6= 48 TOTAL 30 100.0 360

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In our class, the order in which the slices of the pie get organized will matter. In some cases Pie graph slice order seems random. In other cases it can be used to show patterns better.

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Unless otherwise mentioned … for our geography class Draw a pie graph from smallest to largest. Start at the 12 o’clock position when drawing This leaves all the math rounding error for the last and largest slice.

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We will use a Blank Pie Graph that has tick marks every 10 degrees when drawing our PIE GRAPHS. The line position will get calculated and the lines can be drawn based on numbers in a second “organized” table. Each tick mark has a number between 0 and 360. All tick marks go up by 10 as you go clockwise

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90 270 180 10 20 0 30 PIE GRAPHING BLANK

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Category Percent degrees Line Position Brown 13.3 48 Hazel 20.0 72 Blue 26.7 96 Green 40.0 144 TOTAL 100 360 Step 2 – Re-organize original data - Organize from Smallest to largest - This Table will also have 4 Columns - 3 Columns from the previous chart and one new one example: class eye colour Organized Table

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The New column is called line position It will identify the exact position (out of 360 degrees) to draw boundary lines To calculate … add the thickness of the new pie slice to the previous line position above in the table. LOOK at the results in the completed table.

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Category Percent degrees Line position Brown 13.3 48 0 + 48 = 48 Hazel 20.0 72 48 + 72 = 120 Blue 26.7 96 120 + 96 = 216 Green 40.0 144 216 + 144= 360 TOTAL 100 360

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To Draw and Label Pie Graph Blank 1) Start at The top centre = 0 degrees 2) Identify the correct line position using the 10 degree tick marks to find the (in this case 48 degrees is the first line). 3) Draw a line from the centre of the pie to the edge at this exact line position. ( you may have to estimate between ticks )

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90 270 180 20 110 The 48 degree line position 40 50 0

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Find Line position for Line #2 on the pie graph and draw it in Place. (In this case it is at line position of 120 degrees)

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90 270 180 20 110 The 120 degree line position 130

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Find Line position for Line #3 on the pie graph and draw it in Place. In this case it is at line position of 216 degrees

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90 270 180 20 210 The 48 degree line position 220

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When all lines are drawn, it’s time to add some colour and make a legend.

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Your final product should look something like this

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Some other important uses for pie graphs

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