GTECH 201 Lecture 03 Data measurements Data errors

GTECH 201

Lecture 03Data measurements

Data errors

Measurement

The process of obtaining scores for each element for each variable

This can take on a variety of forms – Producing scores (and distributions) of

a widely varying nature The measurement of raw variables

Derived variables and measurement

Measurement of the time component

Measurement of the space component

Measurement of Raw Variables

Primary and secondary data; control over the measurement process

Operational definitions of the measurement process

Highly varied terminology for the different levels of measurement

Derived Variables and Measurement

Why not use raw variables?

Derived variables can be considered as a ratio (or percent or index) of two numbers – the numerator and the denominator (in the ratio a/b, a is the numerator, b is the denominator)

Measurement of the Time

and Space Components Time is a continuous variable

Date, time and datetime

Space is a continuous variable

(x,y) and (x,y,z) location measurement

Distance and bearing alternative

Measurement Scales

Nominal

Ordinal

Interval

Ratio

Most statistical texts follow the original 4-fold measurement structure attributed to a chap called Stevens, written up in 1946:

Geographical Data

Dayta or darta

Data sets used by “geographers”

Geographic vs. spatial data

3 Quick Questions: What would a ‘piece of data’ look

like? Must data consist of numbers? What would a data set look like?

3 Approaches to Data

Definitions

Statistical analysis

Spatial analysis

Data base structures (IT)

The terminology used in handling data sets (in geography) stems from three different sources.

It is now somewhat of a mix of the three.

Some Basic Definitions Element (= observation = entity) – the smallest (measurable) unit Population (of elements) (approximately equal to universe) – the totality of all

elements. May be finite or infinite, with size known or unknown Sample – a subset of the population Variable (= attribute) – a characteristic of the element in which we are interested Data score (or simply datum/data) – an individual value for an element for a variable Data distribution – a set of scores for a variable Data set – an assemblage of related data distributions for a set of elements

Things We Can Do With Data

Data display – a display of a data distribution in the form of a table, graph or map

Data analysis – the analysis of data distributions (including statistical analysis)

Data storage and retrieval – just as the name implies (anything from sheets of paper in a folder to a computer file)

Data Structure

Measurement is the process of obtaining scores for an element

Each element will have an infinite number of characteristics, the relevant ones of which will be measured (the variables or attributes)

The element will also occupy a locational position in time and space; sometimes this position is important, sometimes it is not

Geographic Data Structure

A generalized data structure for each element is:

The data structure that results can be presented (stored) in a data matrix, where the columns are the variables (with or without the temporal and spatial location), and the rows are the elements

{ (var1, var2, ….., vark), (temporal location), (spatial location) }

Introduction to MS Excel

Opening screen

Typical look of an Excel spreadsheet

User Interface Elements Title bar

Menu bar

Toolbars Standard toolbar Formatting toolbar Formula bar Status bar

Worksheets

Name Box

Selecting Cells

Entering and Editing Data Entering Data

Editing Data F2 Double-click Formula

Formatting Text Just as in MS Word

Alignment Bold, italics, underline

Font color

Column Width

Choose Format > Column > Width  

Drag cursor on separation line

Double click on separation line

Holding left mouse pressed

Moving to a New Worksheet

Mathematical Calculations Cell arithmetic

AutoSum

Function button

Functions

Function categories

Function wizard

Formatting Numbers

Choose Format > Cells   Before

Toolbar

After

Deleting Rows and Columns

Creating Borders

Choose Format > Cells 

Border icon on toolbar

Merge and Center

Icon on Formatting toolbar

Autofill

Printing Page setup or Print preview

Creating Charts Step 1 - select the data that you want

charted

Step 2 – pull-up chart the wizard

Modifying Charts

Change size and position

Modify other characteristics