step 1: basics: spatial data and digital maps...shape, its attributes and other information are...
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Written by Robbie Austrums. For help or feedback please e-mail r.austrums@worc.ac.uk
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
Written by Robbie Austrums. For help or feedback please e-mail r.austrums@worc.ac.uk
Examples of Raster Data
Examples of Vector Data
Written by Robbie Austrums. For help or feedback please e-mail r.austrums@worc.ac.uk
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.
Written by Robbie Austrums. For help or feedback please e-mail r.austrums@worc.ac.uk
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)
Written by Robbie Austrums. For help or feedback please e-mail r.austrums@worc.ac.uk
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’:
Written by Robbie Austrums. For help or feedback please e-mail r.austrums@worc.ac.uk
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.
Written by Robbie Austrums. For help or feedback please e-mail r.austrums@worc.ac.uk
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
Written by Robbie Austrums. For help or feedback please e-mail r.austrums@worc.ac.uk
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.
Written by Robbie Austrums. For help or feedback please e-mail r.austrums@worc.ac.uk
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
Written by Robbie Austrums. For help or feedback please e-mail r.austrums@worc.ac.uk
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)
Written by Robbie Austrums. For help or feedback please e-mail r.austrums@worc.ac.uk
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
Written by Robbie Austrums. For help or feedback please e-mail r.austrums@worc.ac.uk
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)
Written by Robbie Austrums. For help or feedback please e-mail r.austrums@worc.ac.uk
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
Written by Robbie Austrums. For help or feedback please e-mail r.austrums@worc.ac.uk
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
Written by Robbie Austrums. For help or feedback please e-mail r.austrums@worc.ac.uk
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
Written by Robbie Austrums. For help or feedback please e-mail r.austrums@worc.ac.uk
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.
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