Gentle Introduction to Programming Part 1

: for GIS Dummies

Hyesop Shin

hyesop.shin@auckland.ac.nz

University of Auckland

May 7, 2025

What will we cover?

Why programme in a GIS course?
Programming Basics
Interactive lecture

Why do we learn to code?

We are not computer scientists (I am not at least)
GISci and Geography disciplines are becoming increasingly quantitative
Large datasets
We want to do our job quickly and do less of the same work.
Programming can also be fun
Programming can help make us better scientists - Open Science

ArcGIS
Programming

Example: Python

What is a computer?

What is a computer - Python

What are computers good at?

Tasks computers are good at include ¹:

Well-defined tasks (i.e. Clear aim, Low Risk of Failure)
Data storage and manipulation
Repetitive calculations
Processing data or instructions (Important!)

What are computers bad at?

Abstract or poorly defined tasks

print("Python" > "R")

False

print("Ronaldo" > "Messi")

True

Tasks requiring impossible computing power (intractable tasks)

## True Pi
3.14159265358979323846264338327


>>> from mpmath import mp
>>> mp.dps = 20    # set number of digits
>>> print(mp.pi)
3.1415926535897932385

Can’t remember what you’ve written (unless you wrote it down somewhere)

We need to be less poetic

and become more direct to the point

Why Python?

1. Python is widely used

Python being 1st in a row in programming (TIOBE Rank)

2. Python is open

Open as in
- free of charge
- as in access (download and run)
- over time
- not closed
- reuse and change
- any place (platform) and for everyone

3. Python is approachable

Modern interpreted languages (Python) – Code is interpreted line-by-line via a programme
Translating high-level human readable code to machine readable code
Scripting
- Only need snippets of code
- Can perform jobs quickly
- Ideal for GIS jobs

4. Python is connected

Geographic Information Systems (GIS) software such as QGIS or ArcGIS now include a Python interpreter built in to the software
Can customise solutions for your specific data analysis needs

5. Python is linked to our GISCI courses & future jobs

ENVSCI 203 Modelling Environmental Systems
GISCI 341 Advanced Remote Sensing
GISCI 343 GIScience Programming and Development
Honours and Postgraduate courses

Industry & Academia & Public Sector…

The War of Coding

FYI: We have plenty of Geocomputation courses in postgraduate courses!
R & Python both have specialties.
FYI: I am an R enthusiast

Interactive Lecture using Python

What we will cover:

Basics
Variables
Loops and basic conditionals
Functions
Geopandas

How will we cover it?

Install Python on your machine
Jupyter lab / Notebook
Google Colab
- “Another” Free service provided by Google
- Live code, text and graphics in one place
- Compatible with multiple languages

Roll your sleeves and let’s get started!

Make sure you are well set up with Google Colab using the URL below: https://colab.research.google.com

I will code here: https://tinyurl.com/gisci242

Basic Programming Concepts

We will cover:

Simple Python maths
Functions
for loops
Conditional Statements
Import files

Simple Python maths

Simple Python maths - answers

1 + 1

5 * 7

2**3

Strings

print("hello world") # print strings

len("hello world") # to count text in Python Shell
print(len("hello world")) # in Google Colab

Maths with modules

sin(3)
sqrt(4)

Did you get the result you expected?

Facing Errors can be daunting

sin(3)
---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-1-acdde95a6016> in <cell line: 1>()
----> 1 sin(3)
NameError: name 'sin' is not defined

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-2-317e033d29d5> in <cell line: 1>()
----> 1 sqrt(4)

NameError: name 'sqrt' is not defined

Python can’t calculate square roots or do basic stats?
Of course it can, but we need one more step.

Solution

import math

math.sin(3)
math.sqrt(4)

Well done! You have just managed to use a math module too!

Combining Functions

Functions can also be combined. The print() function returns values within the parentheses as text on the screen. Let’s print the value of the square root of four.

print(math.sqrt(4))

print("The square root of 4 is", math.sqrt(4))

Variables

A variable can be used to store values calculated in expressions and used for other calculations

temp_celsius = 10.0

print(temp_celsius)

10.0

Data types

A data type determines the characteristics of data in a programme
Basic data types in Python.

Data type name	Data type	Example
`int`	Whole integer values	4
`float`	Decimal values	3.1415
`str`	Character strings	‘Freezing’
`bool`	True/false values	True

Data types

weatherForecast = "Freezing"
type(weatherForecast)

<class 'str'>

Your Turn!

Print the type() of:

- 33
- 8.394
- Windy
- False

Lists

When we have more clothes/items we would like to align similar types of clothes into a drawer

List Example 1

top = ["socks", "underwear", "handkerchief"]
middle = ["T-shirts", "Pajamas", "Trousers", "Shorts"]
bottom = [30, 73, 100, 62]

print(top[0])
print(min(bottom))

socks  # <- index "an element of a list"
30     # <- the smallest element of the list

List Example 2

Let’s first create a list of selected station_name values and print it to the screen.

station_names = [
    "Britomart",
    "Ōrākei",
    "Meadowbank",
    "Purewa",
    "Glen Innes",
    "Tamaki",
    "Panmure",
    "Sylvia Park"
]

station_names

['Britomart', 'Ōrākei', 'Meadowbank', 'Purewa', 'Glen Innes', 'Tamaki', 'Panmure', 'Sylvia Park']

type(station_names)

<class 'list'>

Index values

To access an individual value in the list we need to use an index value.

station_names[1]

'Ōrākei'

Python returns ‘Ōrākei’ instead of ‘Britomart’. Can anybody guess why?

Index values

station_names[2]

'Meadowbank'

station_names[2:5]

['Meadowbank', 'Purewa', 'Glen Innes']

station_names[-1]

'Sylvia Park'

station_names[-8]

'Britomart'

Modifying list values

station_names[-1] = 'Shopping Mall'
station_names

['Britomart', 'Ōrākei', 'Meadowbank', 'Purewa', 'Glen Innes', 'Tamaki', 'Panmure', 'Shopping Mall']

Modifying list values

station_names[-1] = 'Shopping Mall'
station_names

['Britomart', 'Ōrākei', 'Meadowbank', 'Purewa', 'Glen Innes', 'Tamaki', 'Panmure', 'Shopping Mall']

station_names.reverse()
station_names

['Shopping Mall', 'Panmure', 'Tamaki', 'Glen Innes', 'Purewa', 'Meadowbank', 'Ōrākei', 'Britomart']

Modifying list values

station_names.append("new station")
print(station_names)

['Shopping Mall', 'Panmure', 'Tamaki', 'Glen Innes', 'Purewa', 'Meadowbank', 'Ōrākei', 'Britomart', 'new station']

Your Turn!

Define station_names in your environment
Add Otahuhu, Middlemore, Papatoetoe, Puhinui, Manukau as a list (you can Google “Auckland Eastern Line” and find the Wikipedia)
Assign that in your environment as more_eastern
This time, try extend to combine the two lists

station_names = ["Britomart", "Ōrākei", "Meadowbank", "Purewa", 
  "Glen Innes", "Tamaki", "Panmure", "Sylvia Park"]

Documentation

At this point, you might think, Hang on, do I have to memorise everything?
The answer is NO
If you are stuck, visit https://www.python.org/doc
Google your problem (Stackoverflow)
ChatGPT and Gemini (🧐)

`for` loop

Loops allow parts of code to be repeated some number of times
Iterates over all of the items in a Python list and performing a calculation on each item.

`for` loop: concept

for variable in collection:
    do things with variable

Let’s break down the code above to see some essential aspect of for loops:

The variable can be any name you like.
The statement of the for loop must end with a colon (:)
The code that should be executed as part of the loop must be indented beneath the for loop statement.
The typical indentation is 4 spaces.
There is no additional special word needed to end the loop, you simply change the indentation back to normal.

Your daily for loop

for day in my_life:
    wake_up()
    take_shower()
    eat_breakfast()
    brush_teeth()
    ride_beam()
    come_to_lecture()
    ...

for loop: an example

for name in station_names:
    print(name)

Britomart
Ōrākei
Meadowbank
Purewa
Glen Innes
Tamaki
Panmure
Sylvia Park

Different example

european_cities = ["Amsterdam", "Brussels", "London", "Rome"]

for city in european_cities:
    print(city)

Examples using `range`

for value in range(5):
    print(value)

Examples using `range`

group1 = [1, 3, 5]
group2 = [0, 1, 2]

for i in range(2):
    print(group1[i], group2[i])

1 0
3 1

Your Turn!

cities = ["Helsinki", "Stockholm", "Oslo", "Reykjavik", "Copenhagen"]
countries = ["Finland", "Sweden", "Norway", "Iceland", "Denmark"]

The indices of the cities and countries are in the same order
For example, Helsinki and Finland are in index 0
Create a for loop that describes something like Helsinki is the capital of Finland

Examples using two lists - Answers

for i in range(5):
    print(cities[i], "is the capital of", countries[i])
    
for i in range(len(cities)):
    print(cities[i], "is the capital of", countries[i])

Helsinki is the capital of Finland
Stockholm is the capital of Sweden
Oslo is the capital of Norway
Reykjavik is the capital of Iceland
Copenhagen is the capital of Denmark

Conditional statements

We will learn how to make choices in our code using conditional statements (if, else) and Boolean values (True, False).
Conditional statements can change the code behaviour based on certain conditions.
The idea is simple: IF a condition is met, THEN a set of actions is performed.

if else Example 1

temperature = 17

if temperature > 25:
    print("it is hot!")
else:
    print("it is not hot!")
    
print(temperature)

it is not hot

if else Example 2

temperature = 30

if temperature > 25:
    print("it is hot!")
else:
    print("it is not hot!")
    
print(temperature)

it is hot

`if` statement without `else`

The code indented under the if-statement is not executed if the condition is not True. Instead, code under the else-statement gets executed.
How about if without else?

temperature = 17

if temperature > 25:
    print(temperature, "is greater than 25")

Conditional operator

weather = "rain"

if weather == "rain":
    print("Wear a raincoat!")
else:
    print("No raincoat needed.")

Wear a raincoat!

Comparison operators

Operator	Description
<	Less than
<=	Less than or equal to
==	Equal to
>=	Greater than or equal to
>	Greater than
!=	Not equal to

Boolean values

Comparison operations yield Boolean values (True or False).
In Python, the words True and False are reserved for these Boolean values, and can’t be used for anything else.

temperature > 25

False

Combinations

Combining conditions

We can also use and and or to combine multiple conditions on boolean values

Keyword	Example	Description
and	a and b	True if both a and b are True
or	a or b	True if either a or b is True

Combination Example

weather = "rain"
wind_speed = 14
comfort_limit = 10

# If it is windy or raining, print "stay at home",
# otherwise (else) print "go out and enjoy the weather!"
if (weather == "rain") or (wind_speed >= comfort_limit):
    print("Just stay at home")
else:
    print("Go out and enjoy the weather! :)")

Just stay at home

Combining for-loops and conditional statements

We can also combine for-loops and conditional statements.
Let’s iterate over a list of temperatures, and check if the temperature is hot or not

temperatures = [0, 12, 17, 28, 30]

# For each temperature, if the temperature is greater than 25, print "..is hot"
for temperature in temperatures:
    if temperature > 25:
        print(temperature, "is hot")
    else:
        print(temperature, "is not hot")

0 is not hot
12 is not hot
17 is not hot
28 is hot
30 is hot

Summary - What have we learned?

Programming is not too difficult than you think. They are easy to understand and share (and fun!)
Programmes keep a log of the changes you make to your programmes - open science
Python is one of the popular programming languages - we are going to nail this!
Basics of Python
- Basic programming
- Functions
- for loops
- Conditional statements
- Combos of the above

Next week

How to import spreadsheet data
How to clean and use data
Learn it through Pandas module

References

Tekanen et al. (2022), Introduction to Python for Geographic Data Analysis, https://pythongis.org/
Rey et al. (2020), Geographic Data Science with Python, https://geographicdata.science/book
Dorman et al (2023), Geocomputation with Python, https://py.geocompx.org/

Gentle Introduction to Programming Part 1

What will we cover?

Why do we learn to code?

What is a computer?

What is a computer - Python

What are computers good at?

What are computers bad at?

We need to be less poetic

Why Python?

1. Python is widely used

2. Python is open

3. Python is approachable

4. Python is connected

5. Python is linked to our GISCI courses & future jobs

The War of Coding

Interactive Lecture using Python

How will we cover it?

Roll your sleeves and let’s get started!

Basic Programming Concepts

Simple Python maths

Simple Python maths - answers

Strings

Maths with modules

Facing Errors can be daunting

Solution

Combining Functions

Variables

Data types

Data types

Your Turn!

Lists

List Example 1

List Example 2

Index values

Index values

Modifying list values

Modifying list values

Modifying list values

Your Turn!

Documentation

for loop

for loop: concept

Your daily for loop

for loop: an example

Different example

Examples using range

Examples using range

Your Turn!

Examples using two lists - Answers

Conditional statements

if else Example 1

if else Example 2

if statement without else

Conditional operator

Comparison operators

Boolean values

Combinations

Combining conditions

Combination Example

Combining for-loops and conditional statements

Summary - What have we learned?

Next week

References

Thanks! Q & A

`for` loop

`for` loop: concept

Examples using `range`

Examples using `range`

`if` statement without `else`

Thanks!
Q & A