IMPROVING GIS SPATIAL ACCURACY WITH THE GEOGRAPHIC COORDINATE DATABASE Adjusting GIS Data to the GCDB 1

Montana’s Cadastral Data Are Based On & Connected To The GCDB 2

BECAUSE THE GCDB WAS NOT UNIVERSALLY AVAILABLE DURING EARLY MAPPING EFFORTS, MANY BOUNDARY GIS LAYERS WERE CONNECTED TO OTHER GIS REPRESENTATIONS OF THE PLSS. IN ORDER TO CONFORM TO TODAY’S CADASTRAL DATA, AND THE OFFICIAL REPRESENTATION OF THE PLSS (THE GCDB), THOSE DATA MUST NOW BE CONNECTED TO THE GCDB. THIS WORKSHOP WALKS THRU THE STEPS TO CONNECT A GIS LAYER TO THE GCDB. All Boundary Data Should Be Connected to the GCDB 3

BOUNDARY DATA THE OBJECTIVE OF THIS WORKSHOP IS TO INFORM ON HOW TO CONNECT GIS BOUNDARY DATA TO THE GCDB. Objective 4

Workshop Steps Lesson 1: Gather & Organize the resources. Lesson 2: Prepare the data for the adjustment. Lesson 3: Perform the adjustment. Lesson 4: Analyze the results. Lesson 5: Follow up editing. 5

Graphic of the Basic Adjustment Process

GATHERING & ORGANIZING THE RESOURCES Lesson 1 7

Montana’s GIS/GCDB Web Page 8 White Paper PowerPoint Overview PowerPoint Tutorial Adjustment Script Links to GCDB Information Links to GCDB Data. White Paper PowerPoint Overview PowerPoint Tutorial Adjustment Script Links to GCDB Information Links to GCDB Data.

GIS Data to Adjust Reference & Source Data  Boundary GIS layer  GCDB Points (New Control)  Vertices from the Boundary GIS layer (Old Control)  Cadastral Adjustment Script Adjustment Data & Resources 9

Tutorial Data The example GIS data set is Pondera County’s Fire Districts. This dataset is not connected to the GCDB as shown in the accompanying illustration. The goal of this tutorial is to connect this GIS dataset to the GCDB. Pondera County Fire Districts GCDB points GIS Layer vertices not coincident with GCDB 10

Gathering the GIS data sets GIS Data to Adjust 1. Create a project workspace; 2. Copy the boundary data to workspace folder; GIS Data to Adjust 1. Create a project workspace; 2. Copy the boundary data to workspace folder; GCDB Reference Data ftp://ftp.gis.mt.gov/cadastralframework/GCDB Copy the GCDB file to the workspace folder OR … GCDB Reference Data ftp://ftp.gis.mt.gov/cadastralframework/GCDB Copy the GCDB file to the workspace folder OR … 11

Alternatively Connect to the Cadastral Map Service 12 Connect to the GCDB map service via ArcCatalog: gis.mt.gov

Load the source data into ArcMap GIS Data to Adjust 1. Open ArcMap; 2. Add the boundary data to ArcMap; GIS Data to Adjust 1. Open ArcMap; 2. Add the boundary data to ArcMap; 13

Load and prepare the reference data GCDB Reference Data 1. Add the GCDB points to ArcMap; 2. Select the GCDB points that are within ½ mile of the boundary data; 3. Save the selected GCDB points as a shapefile to the workspace folder. GCDB Reference Data 1. Add the GCDB points to ArcMap; 2. Select the GCDB points that are within ½ mile of the boundary data; 3. Save the selected GCDB points as a shapefile to the workspace folder. 14

Add GCDB Points 15

Select the GCDB points that are within ½ mile of the boundary data set. 16

Export the selected GCDB points to a shapefile 17 Make sure that all your data sets have the same spatial reference

Understanding your data 18

PLSS vs. Non-PLSS Boundaries 19

Review your data quality 1. Review the spatial accuracy of the GCDB. 2. Review the quality of alignment of the Old Control to the New Control. 20

About GCDB Accuracy Each GCDB point represents the location of a township, or section, or ¼ section corner. Every GCDB point has an associated X coordinate accuracy estimate, and a Y coordinate accuracy estimate. The GCDB will serve as the reference frame for the boundary data. Therefore the boundary data will be no more accurate than the GCDB. Note: Other GCDB points may exist in some areas that represent locations in original PLSS surveys such as meander points along riparian areas, or mineral survey corners, and others. 21

GCDB Accuracy Fields 22

How to review the spatial accuracy of the GCDB. 1. Right click on the GCDB layer and open its table; 2. Right click on the ERRORN or ERRORE fields and select STATISTICS from the pop-up menu. Your results should look similar to this: 23 The error values are subjective estimates.

This is the range of errors of the coordinates in this GCDB data set. 24

Another way to look at the magnitude and distribution of errors is to map them. 25

PREPARING THE DATA FOR THE ADJUSTMENT. Lesson 2 26

Control Point Files 27 GCDB adjustments use 2 control point files. 1. The New Control is the GCDB (and sometimes additional points). 2. The Old Control comes from either an older GCDB (for data already connected to the GCDB), or from the vertices of the layer to adjust.

Two steps for creating the Old Control Create the points (from the polygon vertices). 2. Assign GCDB IDs to those points. Additional steps and processing may include: Weeding out inappropriate or unnecessary points; Creating non-PLSS control points.

Points From Vertices Points from Polygon vertices: Generate points at the vertices of the polygon layer (Pondera Fire Districts). The points will be separate shapefile of points that will be the basis for the oringination vectors in the adjustment OldControl_NoIDS Call the shapefile OldControl_NoIDS 29

To create a control file from the GIS features… ArcINFO:  ToolboxData Management FeaturesFeature Vertices to Points  Toolbox: Data Management  Features  Feature Vertices to Points– creates a point layer from the polygon, or polyline vertices. ArcEditor or ArcView  Use a third party utility such as ETGeoWizard or XtoolsPro to create a point layer from the polygon, or polyline vertices. OldControl_NoIDs The point layer will be used as the “OLD” control, so name it OldControl_NoIDs (we will add the IDs in a later step) 30

ArcInfo 31 Feature Vertices to Points Save to a file in your workspace. OldControl_NoIDs Name the file OldControl_NoIDs

Alternatively: ET GeoWizard Polygon to Point 32

OldControl vs New Control The Cadastral Adjustment will use the coordinates of the OldControl points and the NewControl points to generate the adjustment vectors. The basis for these vectors is the GCDB ID. Assign the GCDB ID to each point in the OldControl_NoIDs 33 GCDB point Vertex point GCDB point Vertex point

Spatial Join The Spatial Join will assign to each point in the OldControl_NoIDs, the attributes of the GCDB (NewControl) points nearest to it. Join the NewControl to the OldControl_NoIDs New Control GCDB points (red squares) OldControl_NoIDs Vertex points (green circles) 34

Spatial Join 1. Right click on the OldControl_NoIDs in the TOC 2. Joins & Relates 3. Join 4. Select : 5. Join data from another layer based on spatial location 6. Select the NewControl as the layer to join to OldControl_NoIDs Save the new file asOldControl 35 Myworkspace\OldControl

Results of the spatial join GCDB IDs are now assigned to each point in the OldControl., along with the distance* to the nearest GCDB point (shown here in parentheses). However, there may be some duplication, as shown here (and on the next slide). 36 * Note that the distance units returned by this operation are the units set in your data frame’s spatial reference (probably meters).

Dealing with duplicates Here 3 points in the OldControl have the same GCDB ID, however, only one is appropriate. Discuss some ways to deal with this. 37 The distances to the nearest GCDB point are shown in parentheses.

Example solution – Generalize Polygon One way to deal with the duplicate IDs in the OldControl, is to clean up the polygon layer first, in order to eliminate or reduce the number of vertices. This is a good solution in this example because the extra vertices should not be there. Here is the generalized polygon showing the reduced number of vertices. Instead of 3 vertices (green) in the original polygon, there is now only one Vertex (yellow) after generalizing the polygon. Resultant Single vertex (yellow) Originally there were 3 vertices (green) Nearest gcdb point 38

Caution! Double Corners 39 There can be double corners – especially along township lines. Make sure that you snap to the correct corner for each section!

40 Other cleanup and weeding examples

Thin your OldControl File 1. Remove all points that are so far from the nearest GCDB point that they probably are NOT the same point. (use the distance field to identify them, e.g. distance > 60) 2. Remove all the meander points (“PointLab” like ’80%’) 3. Remove other points that are probably not PLSS points. 41

Meanders vs vertices This GIS boundary follows the river in parts.  Here we see the difference between the boundary vertices(green circles) versus the GCDB meander points (red squares). We do NOT want to use the meanders as control points, so we shall remove them (based on the IDs). River Boundary Vertices vs. Meanders 42 Thin your OldControl File Remove meander points:

Meander Points Meander corners are part of the original PLSS surveys along water ways. These points are represented in the GCDB with an 800 number series in the IDs. Meanders typically do NOT represent water boundaries, and should be removed from the control point files. Meanders along waterways are not boundaries. 43

Other points to remove based on GCDB Code (PointLab) GCDB ID CodeRepresents Reserved for software codes Rectangular Surveys Boundaries with Mileposts Riparian Boundaries Tracts Mineral Surveys, Homestead Entries, etc Reserved for software codes 44

Weed by distance Remove meanders and other non essential points How to Weed the OldControl Point File by selecting and deleting records. 45

Notes 1. If you have points in the OldControl that do not have a GCDB ID, those points will not get an assigned adjustment vector. So, the polygons at that location will move an amount that is proportional to its distance to the nearest adjustment vectors. 2. If you have some boundaries that you want to hold fixed in place (e.g. river ways or road ways), then give them dummy IDs and COPY them to the NewControl file. This gives those points (and the polygon edges that follow them) ZERO adjustment vectors. 46

47 Areas that should NOT move can be fixed in place

FIX in Place 1. Select the OldControl points on boundaries that are NOT PLSS, and give them unique, non-GCDB IDS. 2. Then, copy them into the NewControl file. Some boundaries should remain where they are. 48

49 After the cleanup, the files are now ready to adjust

The OldControl Is Now Ready for the Adjustment 50

PERFORM THE ADJUSTMENT. Lesson 3 51

Free(!) Script 52 ftp://ftp.gis.mt.gov/cadastralframework/GCDB/AdjustmentScript.zipftp.gis.mt.gov/cadastralframework/GCDB/AdjustmentScript.zip

Load the Cadastral Adjustment Script 1. Tools  Macros  Visual Basic Editor (or: ALT + F11) 2. In the Visual Basic Editor: (highlight Project) 1. File  Import File  RubberSheetLayers.txt 2. Expand Project  Modules  Module1 [double click on this] 53 TIP: The cadastral adjustment script is a TXT file, so you may need to show ALL FILES in the file browser.

The script Parameters to Modify 54

Cadastral Adjustment Script Obtain & Modify the Parameters in the Cadastral Adjustment Script You should check and/or modify the following: OldControlNewControl  Your dataset names: OldControl, NewControl POINTID  Your field names: POINTID (all caps, no underscore) units  Your radial search parameter (note that the units are the same as the data frame’s units). 55

Application Requirements 56 All datasets must have the same spatial reference/units, etc. Editing must be active on the data workspace. There must be two control point files: Old Control New Control Control point files must both have a POINTID field with matching strings.

 THE DATA SETS HAVE DIFFERENT SPATIAL REFERENCES.  THE NEWCONTROL (GCDB) FILE HAS RECORDS THAT ARE MISSING A POINT ID.  FIELD NAMES IN NEWCONTROL AND OLDCONTROL DO NOT MATCH EACH OTHER.  FIELD NAMES IN NEWCONTROL AND/OR OLDCONTROL DO NOT MATCH THE PARAMETER IN THE SCRIPT.  FILE NAMES FOR NEWCONTROL AND/OR OLDCONTROL DO NOT MATCH THE PARAMETERS IN THE SCRIPT. 57 Some things that could choke the script…

Run the Adjustment 1) After setting your parameters to the appropriate values, Editing 2) Start an Editing session in ArcMap 3) hit the RUN button. BACK UP YOUR DATA! Be sure that you have a copy of your original polygon data, in case something goes wrong. BACK UP YOUR DATA! Be sure that you have a copy of your original polygon data, in case something goes wrong. 58

Results! 59 Original location Adjusted location

ANALYZING THE RESULTS. Lesson 4 60

Polygon movement to the GCDB The vertex moved 5.2 feet here.

FOLLOW UP EDITING Lesson 5 62

Transition Areas 63 TRANSITION AREA BETWEEN PLSS AND NON_PLSS BOUNDARIES: Some additional editing might be necessary after the adjustment when non-PLSS features are boundaries because the linkages from the PLSS to the non-PLSS may be modified by the adjustment. Careful inspection of the adjusted data is very important for data integrity. For example, where a boundary follows a section line to a river as shown below.

Example Transition Area 64 Adjusted boundary (green) snapped to GCDB point Original boundary (orange) Transition area Note: New vertex introduced by adjustment GCDB section line (red)

Detail of Example Transition Area 65 Orangegreen Orange line is before the adjustment, green line is after the adjustment. PLSS Line River Line Transition area - requires review and editing.

For more information contact Montana Base Map Services Center:  Stu Kirkpatrick – State GIS Coordinator   Keith Blount – Geographer Montana Cadastral Mapping Project DOA\ITSD\GIS Bureau  DJ & A, P.C.  Rj Zimmer, PLS  66

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