Digitizing Plat Maps

Objective

This guide was created to aid Housing Developers in formatting their data into a Google Map standard.  The standard is outlined on the Maps Content Partners website (g.co/maps/geodataupload).  This same process can be done using ESRI software as well. 

Setup

Install and Open QGIS

Download QGIS - please note this workflow is also possible in ArcGIS but QGIS is a free, open source alternative.

Open QGIS

  1. From the desktop start menu search for QGIS Desktop
  2. Select QGIS Desktop to open the program 

Installing a Google Basemap

The first Plugin to install is the QuickMapServices (QMS). This addon will allow the addition of Google’s Map-Tiles or Satellite Imagery as a base layer.

Install the QuickMapServices plugin

  1. Locate the Plugins button within the top Menu Bar
  2. Select Manage and Install Plugins from the drop down menu

  1. This will open a new window.
  2. In the Plugins Manager, enter QMS within the search field.
    • Ensure you are searching within the All menu set
  3. Select the QuickMapServices option and press Install Plugin in the lower right hand corner of the menu.

  1. Select the Globe Icon with the Plus symbol within the Toolbar.

  1. Select More Services & Get Contributed Pack
  2. Select OK and Save to close this window

  1. Select the Globe Plus icon again. This time a drop down menu will appear.
  2. Locate the Google menu set and select the desired basemap. Selecting an option will add the indicated feature to the Layers panel.

Enable the Georeferencer Plugin for QGIS

  1. Locate the Plugins button within the top Menu Bar
  2. Select Manage and Install Plugins from the drop down menu

  1. This will open a new window.
  2. Navigate to the ‘Installed’ menu set and ensure the ‘Georeferencer GDAL’ plugin is enabled

Enable Snapping

Snapping assists with ensuring that geometry is properly connected by allowing the placement of vertices or segments to snap to existing nearby vertices or segments. This is helpful for the following examples:

  • Road segments properly intersecting one another
  • Polygons sharing a boundary instead of overlapping
  1. To enable snapping click [Snapping Options...] in the Project menu

  1. This will open the [Project Snapping Settings] window which will allow the user to set snapping parameters between layers

Project Snapping Settings: Layer 

The Layer menu set allows users to determine which layers are affected by snapping.

  • All Layers: Snapping settings will apply to all layers currently in the project
  • Active Layer: Snapping settings will apply only to the active layer
  • Advanced Configuration: Snapping settings can be set for individual layers 

Project Snapping Settings: Snapping Type

The second tab allows users to select which type of snapping to be applied. 

  • Vertex: Allows snapping at Vertex points only
  • Vertex and Segment: Allows snapping at Vertex points or along a segment
  • Segment: Allows snapping along a segment only

Project Snapping Settings: Tolerance Unit

Determine the tolerance unit type from the Tolerance Unit menu. 

  • Px: Sets the tolerance unit to Pixels
  • Meter: Sets the tolerance unit to Meters

Workflow

Georeference Plat Map into QGIS (georeferencer)

Georeferencing uploaded Plat maps allows users to accurately overlay their Plat Maps over the selected Google Maps imagery by identifying reference locations and locking the image to those coordinates.
  1. Open Georeferencer from the [Raster] menu

  1. Click the [Open Raster] button and select the desired plat map image
    1. Plat maps will need to be a supported image file type (png, tiff, jpg, etc)

  1. Once the image has been loaded into Georeferencer click the [Start Georeferencing] button

  1. You will be prompted to set Transformation Parameters for Georeferencing
    1. Set Transformation type to [Projective]
    2. Target SRS should be set to current projection being used
    3. Output raster should specify output location and file name
  2. To begin Georeferencing, create a point in the Georeferencer tool which can be found in Aerial Imagery by clicking a location on the loaded Raster
    1. These points can be the center of an intersection, corner of a building, or a feature such as a fire hydrant so long as the feature in the Raster can be accurately associated with the same feature/location in a projected map

  1. Once a point is made the [Enter Map Coordinates] window will open
    1. If the coordinates for the point are known enter them in the X and Y value boxes
    2. If the coordinates for the point are not known click the [From Map Canvas] button to collect the X/Y coordinates from the current map canvas
    3. The Enter Map Coordinates window will reappear with the coordinate information 
  2. In general the more Georeference points that can be made the more accurately the image will be but try to have at least four (4) points in different areas to best encompass the area in question
  3. Once all georeferencing points are set click the ‘Start Georeferencing’ button again and the Raster will be georeferenced and overlaid in QGIS

Create a New Shapefile Layer

  1. Open the [Layer] menu, navigate to [Create Layer], and select the [New Shapefile Layer…] option.

  1. Enter the setup details for the [New Shapefile Layer]
    1. Specify the save location and the shapefile name under File Name
    2. File Encoding should be ‘UTF-8’ by default
    3. Geometry type will depend on the data represented by the shapefile
    4. The only changes that may need to be made in Additional dimensions is Project CRS which should be set to the current projection
    5. The standard CRS used by Google is EPSG: 3857 - WGS 84 / Pseudo-Mercator

  1. Create the fields for the new shapefile.
    1. Minimum attribute requirements will vary depending on the data represented
  2. Click the ‘OK’ box to create the layer

Community Boundary Polygon

Creating a Community Boundary Shapefile

  1. Following process described in the Create a New Shapefile Layer section with specific alterations:

    1. Geometry type: Polygon

      Minimum attribute requirements for a Community polygon include:
      • Community (Text): the name of the community/housing development
      • City (Text/String): the name of the city the community/housing development is located
      • State (Text/String): the name of the state the community/housing development is located
      • Country (Text/String): the name of the country the community/housing development is located
      • ZipCode (Whole Number/Integer): the name of the Zipcode/Postal Code the community/housing development is located

Draw a Community Boundary Polygon

  1. Select the layer for the community polygon and click the [Toggle Editing] button to enable editing of the community polygon

  1. Click the ‘Add Polygon Feature’ button and trace the community boundary from the plat map

  1. When finished tracing right click on the map and you will continue to the ‘Feature Attributes’ window to apply attribute information to the newly created feature

  1. Once all features have been created and all necessary attributes have been applied to those features click the ‘Save Layer Edits’ button

  1. Once you are finished editing the shapefile click the ‘Toggle Editing’ button to disable editing on the selected shapefile.

Drawing Road Centerlines

Create a new Roads Shapefile

  1. Following process described in the Create a New Shapefile Layer section with specific alterations:
    1. Geometry type: Line

Minimum attribute requirements

  • ST_NAME (Text/String): Full road name 

Optional information

  • CITY (Text/String): Name of the city the road segment is in (if applicable)
  • STATE (Text/String): Name of the state the road segment is in (if applicable)
  • ZIP (Whole Number/Integer): Zip/Postal code the road segment is in (if applicable)
  • AR_RT_FR (Whole Number/Integer): Starting address on the right-hand side, relative to geometry (if applicable)
  • AR_RT_TO (Whole Number/Integer): Ending address on the right-hand side, relative to geometry
  • AR_LT_FR (Whole Number/Integer): Starting address on the left-hand side, relative to geometry (if applicable)
  • AR_LT_TO (Whole Number/Integer): Ending address on the left-hand side, relative to geometry (if applicable)
  • SURFACE (Text/String): Road surface [paved/unpaved] (If applicable)
  • SPEED_LM (Whole Number/Integer): Speed limit (if applicable)

Draw Road Centerlines

  1. Enable editing for the roads layer
  2. Trace the center of road paths from the plat maps

Drawing Parcel Polygons

Create a Parcel Polygons Shapefile

  1. Following process in ‘Create a New Shapefile Layer’ with specific alterations:
    1. Geometry type: Polygon
  2. Minimum attribute requirements
    1. LotNum (Text/String): A unique identifying number for the parcel
  3. If there are addresses associated with the parcel data it can be added to the Parcel features for creating address points later
    1. ST_NUM (Whole Number/Integer): Street Number (Required if available)
    2. APT_NUM (Text/String): Apartment number (if available)
    3. ST_NAME (Text/String): Street name and type (Required if available)
    4. CITY (Text/String): Name of the city the road segment is in (Required if applicable)
    5. STATE (Text/String): Name of the state the road segment is in (Required if applicable)
    6. ZIP (Whole Number/Integer): Zip/Postal code the road segment is in (Required if applicable)

Drawing Parcels

  1. Enable editing for the parcel layer
  2. Trace the parcel areas individually
  3. Be sure to save edits as you digitize the parcels

Include address information with the parcel data if available

Required address components:

  • Street Number
  • Apartment number (if applicable)
  • Street Name
  • City
  • State
  • Zip/Postal Code

Creating Address Points From Parcel Data

  1. For parcel data that includes address information we can generate address points using the ‘Centroids’ tool in QGIS
  2. Open the ‘Centroids’ tool found in the ‘Vector’ menu under ‘Geometry Tools’

  1.  In the ‘Centroids’ tool select the parcel layer for ‘Input Layer’, check the ‘Create centroid for each part’ option, select the save location for the output shapefile, click the ‘Run’ button

  1. After the process completes there should be address points created for every parcel polygon

Compress all files into a Zip folder

  1. Place all created shapefiles into a folder and compress the folder into a .zip file
    1. A single shapefile is comprised of multiple file types:
      1. .dbf (Required)
      2. .shp (Required)
      3. .prj (Required)
      4. .shx (Required)
      5. .cpg (Optional)
      6. .xml (Optional)

Upload to MCP

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