GRAPHS

GRAPHS

1. What Is?

   • They are one of the most useful tools to analyze data.
     • They are representations of numerical data
       • Using lines
       • Using bars
         • to be able to easily visualize numerical or percentage data.
       • areas

2. Types

   • Bar Chart
     • is a type of graph that are used to display and compare the number, frequency or other measure for different discrete categories of data
       • . A bar graph or a bar chart is used to represent data visually using bars of different heights or lengths.
         • You can use a bar graph when you need to compare things between different groups or do track change over time.
     • Use in San Bartolo School
       • The concise example of the use of bar graphs is present in the excel tables to measure academic indicators of each course.
     • What types of data can be displayed using a bar chart?
       • are useful for displaying data that are classified into nominal or ordinal categories
       • Nominal data are categorized according to descriptive or qualitative information such as county of birth, or subject studied at university
         • Ordinal data are similar but the different categories can also be ranked, for example in a survey people may be asked to say whether they thought something was very poor, poor, fair, good or very good
     • Different types of bar charts
       • Horizontal bar charts
         • are normally drawn so that the bars are vertical which means that the taller the bar, the larger the category. However, it is also possible to draw bar charts so that the bars are horizontal which means that the longer the bar, the larger the category
       • Grouped bar charts
         • Are a way of showing information about different sub-groups of the main categories. In the example below, a grouped bar chart is used to show the different schemes (sub-groups) by which different categories of household materials are recycled.
   • Pie Chart
     • Is a circular graph that shows the relative contribution that different categories contribute to an overall total. A wedge of the circle represents each category’s contribution.
       • such that the graph resembles a pie that has been cut into different sized slices.
       • Every 1% contribution that a category contributes to the total corresponds to a slice with an angle of 3.6 degrees.
     • What data can be presented using a pie chart?
       • charts are a visual way of displaying data that might otherwise be given in a small table
       • charts are good for displaying data for around 6 categories or fewer.
         • When there are more categories it is difficult for the eye to distinguish between the relative sizes of the different sectors and so the chart becomes difficult to interpret.
       • are generally used to show percentage or proportional data and usually the percentage represented by each category is provided next to the corresponding slice of pie
   • Histograms
     • are a special form of bar chart where the data represent continuous rather than discrete categories. In a bar chart the length of the bar indicates the size of the category.
       • but in a histogram it is the area of the bar that is proportional to the size of the category.
         • This difference is due to the fact that in a histogram both the x- axis and y-axis have a scale, whereas in a bar chart only the y-axis has a scale
     • Histograms and Excel
       • The spreadsheet package Excel does not include histograms amongst its standard chart types. It is however, possible to draw basic histograms using Excel by selecting either the column or bar chart types.
   • Line Graph
     • As a line chart, is a type of chart used to visualize the value of something over time. For example, a finance department may plot the change in the amount of cash the company has on hand over time.
     • Are use to
       • are used to track changes over short and long periods of time. When smaller changes exist, line graphs are better to use than bar graphs. Line graphs can also be used to compare changes over the same period of time for more than one group.
   • Scatter plots
     • is a two-dimensional data visualization that uses dots to represent the values obtained for two different variables - one plotted along the x-axis and the other plotted along the y-axis
       • For example, a scatter plot could be used to present information about the examination and coursework marks for each of the students in a class.
       • For example this scatter plot shows the height and weight of a fictitious set of children.

3. ELEMENTS

   • Chart area
     • defines the boundary of all the elements related to the graph including the plot itself and any headings and explanatory text
   • Plot area
     • The plot area is the region containing the data. It is bounded by the x- and y-axes to the bottom and left side.
       • The frame can be completed by drawing around the top and right sides too, but this is not essential.
   • The x-axis:
     • is the horizontal line that defines the base of the plot area. Depending upon which type of graph is being considered different locations on the x -axis represent either different categories (such as years) or different positions along a numerical scale
   • Gridlines
     • are the vertical and horizontal lines placed within the plot area to help read values from the graph. The gridlines should be subtle and not detract from the data.
   • Title
     • All graphs should include a title that summarises what the graph shows. The title should identify what is being described (e.g. speeding offences detected by automatic cameras).

4. 3D effects

   • based graphing packages offer the possibility of producing graphs and charts with a 3D effect. However, in general the use of 3D makes it much more difficult to interpret the data presented in chart or graph
     • because the false depth and perspective that are added to the chart make reading and comparing values extremely difficult.