lesson 3: introduction to using qgis

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Lesson 3: Introduction to Using QGIS

INTRODUCTION Once you have downloaded and installed QGIS, you may notice that there are quite a few files and folders included with each county. There are two main types of files: • Data files include necessary information for each layer in QGIS

o There are two formats: Shapefiles (vectors) or Raster files. A Shapefile is a digital vector (non-topological) storage

format for storing geometric location and associated attribute information.

Raster graphics are digital images created or captured (for example, by scanning in a photo) as a set of samples in a given space. A raster is a grid of X and Y coordinates on a display space and, for three-dimensional images, as a Z coordinate.

• Project files tell QGIS which layers to retrieve and what order to load them. The main project file for the county is called a Base map.

**Warning: You should never save over the Base Map! Always save each property as a new project file.

CONTENTS In this document, you will find instructions for: • Getting to know QGIS • Starting a new project

GETTING TO KNOW QGIS

Instructions

Step Action 1 A project file has been prepared for each county. Navigate to

the QGIS Data folder (in your My Documents folder or C:\ drive) and open the county Base Map. The extension for this file is .qgs (do not confuse it with .qgs~). The example used on the next page shows Allegany county but other counties will be similar.

2 The interface for QGIS will open.

The sections outlined above in red squares are described below:

• Menu toolbar – includes various drop-down menus • Browser Panel – can be used to load layers. You can

turn it off by clicking on the “x” in the upper right corner of the panel.

• Layer Panel – allows you to rearrange and choose which layers are displayed on the map canvas

• Map Canvas – displays the layers and associated data. It has a specified projection

*Note: You can choose which panels and toolbars display (or turn any Panels on if you accidentally turned it off!).

Menu Toolbar

Map Canvas Layers Panel

Browser Panel

• For panels, go to “View” on the Menu toolbar, and then click on “Panels”. Anything with an “x” in a small box next to it will be turned on. Click on the small boxes to turn Panels on or off.

• For toolbars, go to “View” on the Menu toolbar, and

then click on “Toolbars”. Anything with an “x” in a small box next to it will be turned on. Make sure the “Manage Layers Toolbar” is turned on.

3 The Tools that you will be using most frequently are described below and shown on the following page. Moving the cursor over any icon will provide a short description of the tool. The icons most used by the advisor are numbered: 1. Pan: Click and hold the map to shift it. 2. Zoom In: Draw a box around the area to be included in the

Map Canvas. 3. Zoom Out: Draw a box to determine how much more

should be included in the Map Canvas or click once to expand to a much wider geographic region.

4. Zoom to the selected Layer: If a layer is highlighted in the Layers Panel, this icon will zoom to the boundaries of the layer.

5. Previous Zoom: Use this icon to go back to the previous zoom.

6. Information (also called Identify Features): If a layer is highlighted in the Layers Panel, click on this icon and then click on a feature in the Map Canvas. A window will pop up with information about the feature.

a. For example, if the Property Lines layer is highlighted, use the Information tool to click on a

property. A window will pop up with the Tax Account ID information in the top line. To close this window, click on the “x” on the top right.

7. Measuring Tool: This can be used to measure length (such as distance between elevations or distance to water) and and area (such as acres).

8. Add Vector Layer: A vector file comes in many different formats. Advisors will use shapefiles but more often will use keyhole markup language (.kml) to load saved farms from Google Earth (Lesson 4).

9. Add Raster Layer: This will not be used often by advisors but it is the tool used to load the aerial photographs.


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4 The project file for each county should have pre-loaded layers. The layers with an “x” next to them will be visible in the Map Canvas. If the “x” is not visible, the layer is currently turned off. You can turn these on and off at will. Descriptions of the layers are below: • MDA 4-Digit Watershed Codes: This layer is turned off

initially, but once you are zoomed into the property you are working on, you can turn this layer on to see the 4-Digit watershed code that is needed for the plan.

• Property Lines: This is a large file that is turned off initially. Once you have zoomed into the property, turn this layer on to show the property lines in black.

• Waterbodies folder: This folder includes several layers of water features. By clicking on the “+” next to the folder, you can maximize the list to see all layers.

• Buffers folder: This folder includes all 10 and 35 foot setback buffers required for water of the State. Again, you can maximize the folder to see all associated layers by clicking on the “+” next to the folder.

• 100’ Buffers for CAFOs folder: This folder is only available for counties on the Eastern Shore.

• Contours folder: This folder contains the contour layers needed for determining PSI and PMT.

• County Roads: This layer shows the county roads. • County Outline: This layer displays the county line. • County Six Inch Image: This is a high resolution (1 pixel = 6

square inches of land) aerial photograph of the county. It is a very large file, so it is suggested to only turn it on once zoomed into the property.

• County NAIP Image: This is a lower resolution (1 pixel = 1 meter) aerial photograph of the county. Depending on the size of the farm, it may be sufficient for your needs.

5 Other things to note: • Data layers are on top of each other. Layers at the bottom

of the list in the Layers Panel appear on the bottom of the map canvas. For example, if “Ortho” is moved from the bottom to the top, none of the other layers will be seen on the map canvas, even if they have an “X” in the box.

• The “Render” box under the Map Canvas controls whether

selected layers are loaded immediately or when the user has decided what layers need to be shown. For example, if the advisor wants to turn on or off several layers, it is best to turn off “Render” (unclick the X), select what layers should be turned off or on, and then click the “Render” box to refresh the map canvas with the desired layers. This could save a great deal of time when loading the large Contour layers because the program will refresh the map canvas with every layer the user selects or unselects.

STARTING A NEW PROJECT

Instructions You should never save over the original county Base Map on your computer. After opening the Base Map, always “Save As” a new project in the “Projects” folder.

Step Action 1 Open the county Base Map from the QGIS Data folder.

2 Once open, click on “Project” in the menu toolbar, then on “Save As”.

3 Navigate to the QGIS Data folder and double click on the “Projects” folder.

4 Enter a descriptive name (one that includes the operator’s name) as the File name then click on “Save”.

5 Now you can begin working on your project without worrying about saving over the original Base Map.

Updated 2/6/2020