GIS Workbook #2 Data frames, layers and symbology Helen Goodchild

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Data frames When you create a map it will automatically contain a single data frame in which to store and arrange the GIS layers. By default this is called Layers.

The properties of this data frame can be altered, and other data frames can be added to compare datasets.

To access the properties, go to View > Data Frame Properties

Under the General tab, you can change the name of the layer and the units you are working in, and under the Coordinate System tab you can set the projection you would like to work in.

To add a new data frame to the project go to Insert > Data Frame. The new frame will appear in the TOC and will be automatically activated.

EXERCISE 2.1

Re-open the Project file you created in the previous workbook.

Open the Data Frame properties and rename the Data Frame as Study Area. Set the map/display units to meters.

Under the Coordinate System tab, set the projection to UTM 33N. This is located in the folder tree at:

Predefined > Projected Coordinate Systems > UTM > WGS 1984 > Northern Hemisphere > WGS 1984 UTM Zone 33N

EXERCISE 2.2

Add a new Data Frame and add these files, displaying them in this order:

• Rome_pt

• Italy

Rename the data frame Overview map, and give it the same map units and coordinate system as before.

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Only one frame can be active at a time. To switch between the two data frames, right click on the name in the TOC and select Activate.

Attribute data Much of the data in GIS has what we call attributes. For vector data this is held in an accompanying database table, which can be accessed by querying the data, or opening the table directly.

To open an attribute table, right click on a layer and choose Open attribute table.

EXERCISE 2.3

Activate the Study Area data frame and right click on the allsites layer to open the attribute table. This file contains interpreted field survey data for periods from the Archaic (8th-6th centuries BC) to the Early Imperial (1st century AD). Close the table when you have finished.

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Changing Symbology The appearance of the different layers can be changed based on its attributes using Symbology.

To access the symbology of a layer, right click it and choose Properties, then go to the Symbology tab.

For vector data you have the option to display either:

• Features (single symbol)

• Categories (unique values)

• Quantities

• Charts

• Multiple Attributes

To display all your features the same way:

1. Click Features. Because Single symbol is the only option, ArcMap automatically selects it. 2. Click the Symbol button to change the symbol.

The Symbol Selector dialogue box that then appears depends whether your layer is a point, line or polygon.

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In all cases you alter the appearance in the same way. You can either choose a preset option (3), alter the symbol yourself, or a combination of the two, using the colour and weight options on the right hand side of the box (4). Further alterations can be made using the Properties (5).

EXERCISE 2.4

Turn off the visibility of all your layers except roads and rivers, then change the symbology of your layers as follows:

Rivers: Feature > Single symbol. Choose the preset River option in the Symbol Selector box. Change the width of the line to 1.25 and the colour to pale blue (fourth from right, fourth from bottom in the palette).

Roads: Feature > Single Symbol. Choose Arterial Street from the presets, but this time change the colour to grey. Click the Properties box. Under Type choose Simple Line Symbol. In Style, choose Dotted.

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To display different attributes in different ways: 1. Click Categories. ArcMap automatically selects the Unique values option. 2. Click the Value Field dropdown arrow and click the field that contains the values you want to

map. 3. Click the Colour Ramp dropdown arrow and click a colour scheme. 4. Click Add All Values. This adds all unique values to the list. Alternatively, click the Add Values

button to choose which unique values to display. 5. If you want to edit the default label so more descriptive labels appear in your legend and the

table of contents, click a label in the Label column and type the label you want

You can also change each symbol independently by clicking directly on the symbol in the list (6) to change its appearance.

Saving and loading symbology schemes If you have created a complex symbology, you can save this for future use by right clicking on the layer name in the TOC and choosing Save As Layer File. A layer file contains no data, it is simply a legend file describing the appearance.

To load a saved scheme, open the layer properties and under the symbology tab click the import button at the top right.

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EXERCISE 2.5

Turn on the visibility of allsites, then change the symbology of your layer as follows:

Allsites : Categories: Unique values. Choose EARLY_IMPE as your Value field. Add all values.

Uncheck <all other values>

Double click each entry to change its symbol to the following:

Farm: Choose the Circle 1 preset. Change the size to 10. Leave the colour as black.

Farm?: Choose Circle 1. Click Properties and change the Type to a Simple Marker Symbol. Change the Colour to grey and check the box to use an outline. Change the colour of the outline to black. Go back to the original box and change the size to 6.5.

Villa: Choose Triangle 1. Change the size to 18.

Remove all the other categories by selecting them in the window and clicking Remove.

Roads: Feature > Single Symbol. Choose Arterial Street from the presets, but this time change the colour to grey. Click the Properties box. Under Type choose Simple Line Symbol. In Style, choose Dotted.

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To create complex symbology You can create multi-layered symbology using the Symbol Selector. This is particularly useful for polygon files. This example shows how to make cross hatching.

1. In the Symbol Selector dialogue box click Properties 2. Click the plus button to add a new layer 3. In the Type dropdown box, choose Line Fill Symbol 4. Change the angle to 45 5. Change the separation to 3 6. Add another layer using the plus button and make this a line fill symbol. 7. Change the angle to 315 and the separation to 3.

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EXERCISE 2.6

Turn on the visibility of landuse, then change the symbology of your layer as follows:

Landuse : Categories: Unique values. Choose CLASS as your Value field. Add all values.

Uncheck <all other values>

Double click each entry to change its symbol to the following:

Arable: Choose the preset Green option, then add cross hatching (as above) in Spruce Green. Make the outline No Colour (click on the button in the Symbol Property editor)

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EXERCISE 2.6 cont.

Mixed farming: The same as for arable, except leave the separation at 5.

Pasture: Choose the Open Pasture preset, but make the Fill Spruce green and the outline No colour. Go to properties and change the background to Lime dust.

Urban: Choose the 10% ordered stipple preset, but make the outline No colour. In properties make the foreground medium grey, the background very light grey, and the outline no colour.

Woodland: Choose the Scattered Trees 1 preset, Fill colour Spruce Green and outline No colour, then go to properties. Change the background colour to Apple Dust.

Save this Symbology, by right clicking on the landuse file in the TOC and choosing Save as layer file. Call it landuse.

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Labelling data Labels can be added to data as long as it is present in an attribute table.

1. To do this bring up a layer’s properties and go to the Label tab. 2. Check the box at the top to Label features in this layer 3. Choose which attribute you wish to use as a label in the central Text String box. 4. You can change the font/size/etc in the Text Symbol section 5. You can change the placement of the labels by clicking the placement properties button

EXERCISE 2.1 Turn off the sites layer and turn on the toponyms layer. Look at the attribute table for the toponyms. Note which field holds the label. Bring up the properties and add the place names as labels. Make them positioned centrally over the top of the point by using the placement properties. Change the symbology of the point to a circle size 2.

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Raster Data Raster data can be displayed in various ways:

• Unique values or Colormap (Discrete categorical data)

• Stretched (Images or continuous data)

• Classified (Images or continuous data)

• Discrete colour (Discrete categorical data)

Unique Values

Use Unique Values when you want each value in the raster layer to be displayed individually. For instance, you may have discrete categories representing particular objects on the earth’s surface, such as soil types or land use.

The Unique Values renderer displays each value as a random colour. If your data has a ‘color map’, you can use the Colormap renderer to display your data with assigned colours.

Colormap You use the Colormap renderer as you would the Unique Values renderer, except that you choose to have the values in the raster layer represented by a pre-specified colour. This displays automatically.

Stretched The Stretched renderer displays continuous raster cell values across a gradual ramp of colours. Use this when you want to draw a single band of continuous data, such as spectral imagery, aerial photographs, or elevation models.

RGB Composite Use RGB Composite for a multiband raster layer (e.g. satellite images). You can draw a three-band composite of raster data with the option of displaying fewer than three bands or changing the band combination.

Classified The Classified renderer groups cell values into classes. It is typical to use this type of thematic classification on continuous phenomena, such as slope, distance, or suitability, where you want to classify the range into a small number of classes and assign colours to those classes.

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EXERCISE 2.9

• Av-dem will probably appear as a grey rectangle using the stretched renderer

• Make sure you can see the full extent of the files, then bring up the properties for av-dem. Firstly we will correct the stretch. Under the Symbology tab, make sure “Stretched” is selected in the left hand bar, then scroll down in the main window to find the section called “Stretch”

• Make sure you have the stretch type set to “none”, but in the box below, change the Statistics to read “from current display extent” and Apply.

You should now see the elevation more clearly.

• Go back to the properties and try different stretches. For example, try Standard Deviations and type different numbers into to “n” box to see what difference it makes.

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EXERCISE 2.10

Now we will try using a Classified renderer.

• Open the properties of av-dem and choose “Classified” on the left hand side.

• You have the option of choosing how many classes you would like. In this instance we know from the raster information that the elevation goes from 95-247m above sea level. We would therefore like to divide into regular intervals of 50m (4 classes).

• Press the classify button to bring up a new window.

• Choose 4 classes then pick “Manual” as your method

• In the break values box, select the numbers visible then type your own instead: 100, 150, 200, 250 > OK & apply

• You might decide you’d prefer more categories. Try this again with using defined intervals and type ‘50’

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Displaying transparency It is possible to make certain layers slightly see-through, to enable interpretation of data.

1. Bring up the layer properties by clicking on the layer in the TOC, and go to the Display tab. 2. Select the percentage transparency you desire by typing into the Transparent box and

clicking to apply.

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EXERCISE 2.8

Turn on the landuse layer and change the transparency of the layer to 70%

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Your finished map should look similar to this:

Save your project.