Step 1: Basics: Spatial Data and Digital Maps...shape, its attributes and other information are stored separately. Attributes Both vector shapes and raster grid cells possess attribute

Written by Robbie Austrums. For help or feedback please e-mail [email protected]

Step 1: Basics: Spatial Data and Digital Maps

There are two basic types of GIS data: Gridded “Raster” data and “Vector” shapes

Raster Data Raster data, like a digital photograph, is composed of a grid of cells or ‘pixels’. In fact, digital

photographs are a form of raster data supported by GIS, which allows us to incorporate scanned

maps, aerial photographs and satellite images into our datasets. Other forms of raster data have a

property other than colour associated with each cell; perhaps altitude, slope, rainfall or

temperature.

Raster format is best for datasets that vary continuously over an area.

Vector Data Vector data is composed of individual shapes, each possessing its own attributes. There are three

types of vector shape:

Points are dots on the map

On a map of the UK, towns may be represented as point data. Each town point might possess

as attributes its name and population

Polylines are linear shapes composed of straight line segments joined end-to-end

On a map of the UK, roads may be represented as polyline data. Each road polyline might

possess as attributes its name (e.g. A38), type (e.g. A Road) and speed limit

Polygons are area features whose boundary is defined by a series of straight line segments

On a map of the UK, counties may be represented as polygon data. Each county polygon might

possess as attributes its name, its area and the name of its county town

Vector data is most often provided or created as a ‘shapefile’. A single shapefile is actually composed

of several computer files with the same name but different extensions (types). This is because the

shape, its attributes and other information are stored separately.

Attributes Both vector shapes and raster grid cells possess attribute data. These attributes can be of various

types, such as text (for a town name), colour (for an image pixel) or a number (‘integer’ for whole

numbers, ‘float’ for fractions). Each dataset has its own attribute fields (e.g. Name, Population, etc.),

and each map element (point, line, polygon or pixel) has its own value for each field (e.g. Name =

“Worcester”, Population = 90000, etc.)

One shapefile


Examples of Raster Data

Examples of Vector Data


Step 2: Setting up a map document

Follow these steps each time you create a new ArcMap file. This will help you keep track of your

map’s data sources and avoid lost layers (red exclamation mark syndrome)

Upon opening ArcMap 10, you should be greeted by a screen similar to the one below:

To create a new map:

1. Select ‘New Maps’ in the left-hand panel, then select ‘Blank Map’ in the main window.

2. The drop-down near the bottom of the window allows you to select a default geodatabase for

your map. A geodatabase is a container or repository for GIS datasets. You probably don’t have

one for your project yet, so leave this as it was and we’ll set this up in a subsequent step.

3. Press OK

The ‘Getting Started’ window will vanish, leaving you with the normal ArcMap window, which will

look similar to the screenshot overleaf.


The default ArcMap window. See Step 3 for an introduction to the ArcMap interface

There are 4 further steps that will make your map easier to work with:

1. In the ‘File’ menu select ‘Save As’. Navigate to a place on your computer where you want

you map to be stored (e.g. My Documents, or a USB drive). Then create a new folder into

which you can store your map along with all its data sources (named ‘HabitatGIS’ in the

example below). Then double-click on your new folder (I will refer to this as your project

folder) and save your map inside.

2. In the Catalog window on the right-hand side of the ArcMap screen (click in the toolbars

if Catalog is not there), the top item will be ‘Home’ – the folder in which you saved your

map. Right click on ‘Home’ then select ‘New’ then ‘File Geodatabase’.

Menus Toolbars

Auxiliary

windows

Data frame

Table of

Contents

(TOC)


a. Right click on the new geodatabase and select ’Rename’ to give it a more descriptive

name (e.g. HabitatGDB)

b. Right click on the new geodatabase again, and this time select ‘Make Default

Geodatabase’. This will now be the place new data layers are sent by default.

3. In the ‘File’ menu select ‘Map Document Properties’:


Tick the ‘Store relative pathnames’ checkbox. This allows the map to locate its data sources

after being transferred to a different PC (so long as you move the map and its data

together). This will be easiest if you save all the maps data sources into the project folder or

the project geodatabase you created earlier.

4. Finally, right click anywhere in the Data Frame (or on ‘Layers’ in the TOC) and select

‘Properties’. In the ‘Coordinate System’ tab select an appropriate coordinate system, most

likely ‘British National Grid’ (under Predefined->Projected->National Grids->Europe).

You now have a new GIS project comprehensively set up and ready to start work on.

Just remember to place all your GIS data into the same folder as your map. You can use subfolders,

such as “OS_Mapping”, “Shapefiles”, “DEM”, etc. to keep things organised.


Step 3: Finding your way around ArcMap 10

These icons

activate

auxiliary

windows

The current

map scale

The Catalog window

is for managing data

and adding it to your

map

The Toolbox window

contains extension

tools for specialised

tasks

These icons allow you to

switch between Data

view and Layout (page)

view

The Table of Contents (TOC)

shows what data sets are in

your map. Icons at the top

change how they are listed

(e.g. by draw order, location

or visibility)

Add or remove icon

toolbars using the

Customize->Toolbars menu

Use the pin icon to

toggle auto-hide

on these windows

The layout view

shows your page as

it will appear when

printed

These numbers

show the current

coordinates of the

mouse cursor


Dragging a window brings

up docking options (pale

blue arrows) – Drop the

window onto one of these

icons to dock it onto an edge

of the window

These icons dock the

window within the area

occupied by the window

that is currently beneath

the mouse cursor

These icons dock the

window to the edge of the

main ArcMap window.

Try out the options yourself

to see how they work

File options: New,

Open, Save & Print

View options: Zoom,

Pan, Zoom Extents (i.e.

show everything),

Previous Extents (i.e.

undo last zoom)

Select

features or

clear

selection

Editor – For

modifying your

data layers

Georeferencing – For

correctly positioning

data within your map

Add data layers

to your map

Show Editor tools

(see below)

Identify features,

measure distances,

find features

Remember, you can add and remove toolbars

using the Customize->Toolbars menu.


Step 4: Making Maps Part 1: Adding and symbolising data

There are several ways to add data layers to your map. The simplest are:

1. Click the ‘Add Data’ icon on the toolbars, then browse to some data files to add them

2. Drag data files from the Catalog window into either the Data Frame or the Table of Contents

The new data layer will be added to your Table of Contents:

Add data layers

to your map

Drag data into

your map

‘List by Drawing Order’ shows you

which layers will appear above

others (lower layers may be hidden

by higher ones)

A layer’s name is shown next to a

checkbox (tick), which allows you

to turn the layer on and off

Below the layer name is a

representation of how it is being

displayed in your map


When you added a data layer, ArcMap by default displays all the features within that layer in the

same way. The Symbology options allow you to distinguish between different features by looking

at their attributes.

Right-click on the layer name in the Table of Contents and select ‘Open Attribute Table’ - This shows

what data is included within the layer. Rows in the table represent features (each is a single object

on your map), columns represent data ‘fields’ (categories of information available for each feature).

To Change how you data layers are displayed in your map, right-click on the layer name in the Table

of Contents and select ‘Properties’. Alternatively you can just double-click on the layer name. When

the layer properties window appears, select the ‘Symbology’ tab.

Each row in this

table represents

a section of river Each column in this

table represents an

attribute.

In this case, the

‘Legend’ attribute

contains a type

category and may be

useful for displaying

different kinds of

rivers

Here I have chosen to

symbolise the rivers

based on the ‘Legend’

attribute.

Clicking ‘Add All

Values’ puts all

available river types

into the list of

categories

The ‘Show’ panel

on the left of the

window gives

different methods

of symbolising

data.

‘Categories’ is good

for data split into

different types (e.g.

habitats, land use,

or geology)

‘Quantities’ is

better for

numerical data

(e.g. Population,

area, or altitude)


Symbolising Raster Data For raster layers the symbology tab will look a little different. In fact different types of raster layer

will give you a different set of options. A simple raster with just one band will give you this screen:

There are 4 options in the 'Show' panel:

Unique Values - This is for raster layers where each raster cell has

one of a few values that represent categories. For example a land-

use raster, where 1 means 'Urban', 2 means 'Woodland', etc.

Classified - This is for raster layers where each cell possesses a

numerical quantity, but you want to display it as distinct categories.

For example if you have a slope raster and want to display steep

areas (>20°) as red and gentle areas (<20°) as green.

Stretched - This is also for raster layers where each cell possesses a

numerical quantity, it displays each pixel as a colour on a scale from

low to high values.

Discrete Colour - This mode takes a raster where each cell possesses

a numerical quantity. It will round each value to the nearest integer

(whole number) then give each value a random colour.

Stretched

Classified


If a raster layer contains more than one band, then the symbology tab will look as follows:

Now there are only 2 options:

Stretched - This works exactly the same as stretched for single band raster layers, except you have to

specify which band to display (only one gets drawn).

RGB Composite - This creates a colour image from 3 of the bands in the raster layer. You specify

which band is shown in which colour. If you show red as red, green as green and blue as blue then

you get a 'true colour' image, otherwise you get a 'false colour' image. This is often used to include

invisible infrared or ultraviolet light into your map (see below)


Step 5: Making Maps Part 2: Creating a page layout

In ‘Layout View’ you can arrange map elements on a page to produce high

quality printed output

In the ‘File’ Menu select ‘Page and Print Setup’ to change the page size and orientation:

Click this icon to activate Layout View

Choose the printer

you intend to use

(optional)

Choose a page size

Choose a page

orientation


By default, your layout contains just one map element: a Data Frame.

This is the area of your page that will contain a scaled representation

of you map data. Other map elements can be added using the ‘Insert’

menu (see right). The most frequently used map elements include:

Title: Give your map a title that expresses its content

Text: A label or note (e.g. Credit or references)

Neatline: A rectangle around other elements

Legend: Tell the viewer what map symbols represent

North Arrow: Show which way is North on your map

Scale Bar: Show how distances are represented in your map

Scale Text: The scale of your map, e.g. “1:25,000”

Picture: An image file, perhaps a location map exported from another ArcMap file

All of these map elements can be modified by selecting them using the ‘Select Elements’ tool in

the toolbars. You can then move the element by dragging it when the mouse cursor changes to ,

and resize it by dragging the blue corner boxes ( ). Further options are available by right-

clicking any element and selecting ‘Properties’.

Title

Data Frame

Picture (exported

from another

ArcMap file)

Neatline

Scale Bar

Legend

Paper outline

Printable area

Scale Text

North Arrow

Text


Creating a Legend The map legend in particular has a large number of options to modify in order to get it looking right.

When adding the legend it is easiest to accept all the default settings, then, once it has been added,

edit its properties (double-click on it or right-click and select ‘Properties’). That way you can tweak

the options then press ‘Apply’ to see the effects of the changes as you make them.

Untick this if you

don’t want a

legend title

Legend Title -

Sometimes it can

look good to put

your map title in

here

Change the text

font, size, colour

etc. for your

legend title

Change the way

line and area

symbols are

represented on

your legend

To add a layer to

your legend,

select it here and

click [>]

To remove a

layer from your

legend, select it

here and click [<]

To modify how a

layer is displayed

in your legend,

right-click it here

select Properties

then the General

tab (see overleaf)

Use these

buttons to

change the order

if items in your

legend

Change the way

items are spaced

in your legend

Choose whether

invisible layers

are still included

in your legend


Use these to

alter how lines

and areas are

represented in

the legend

Use the top options to change

what layer information is

displayed and how. (In this

example Layer Name is ‘Terrain

Altitude’, Heading is ‘VALUE’

and Labels are ‘1 – 100m’ etc.)

Use this to put a

box around your

legend

Use this to put a

solid background

behind your

legend

Use the gap

options to make

the box wider (x)

or taller (y)

Change the

colour of your

legend border

Round its corners

Change the

colour of the

background

Round its corners

A Drop Shadow

can give your

legend a 3D

appearance

Use the Position

and Size options if

you want to

precisely place

your legend

Remember to

press Apply as

you tweak any of

the settings to

update the

legend and see

what differences

you have made.