Geographic Information Systems

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Maps By Mitch

Parcel Updates - In the beginning...

November 29, 2012

Welcome to "Maps By Mitch". A "blog" of sorts to highlight various maps and the techniques used to create them. I hope to have a new "map" posted on a monthly basis.

When asked what I do as a profession I answer that I am a GIS Technician for Columbia County, which often returns blank stares. Over the next several months we will be giving a peek into the duties of a GIS Technician at Columbia County. The primary responsibility of a a technician is to edit and maintain geographic data. In this example, I will be demonstrating the first of many editions highlighting the updating of the counties parcel layer using an approved/recorded subdivision plan from the Columbia County Planning Commission.

The first step in updating the parcels layer is to add the subdivision to the map.  Why? There are several methods to accomplish this; however, I will draft the subdivision using the bearings and distances provided. Below is a screen shot of a typical subdivision plan. Areas of the survey have been blackend to hide identities but to demonstrate the concept. As previously mentioned, I will add this subdivision into ArcMap via the bearings and distances provided.

First, you need to locate where the subdivision is to be placed. This can be accomplished by using existing landmarks, such as road name(s) or adjacent property owner names, or the Parcel Identification Number (PIN) given by the Columbia County Assessment Office. In this example, I used the owner name to locate the parcel to be subdivided.

As seen on the subdivision plan, the boundary lines contain bearings and distances. They appear in a degrees, minutes, and seconds format, such as: N 20.16’21” W 162.92 FT. In order to add this data into ArcMap, I used the Coordinate Geometry Tool (COGO). As seen in the graphic below, the data is added as a bearing of ‘N20.1621W’ with a distance of ‘162.92’. Because this plan contains more than a single lot, I drafted the outside perimeter first.

Once the outside was complete, the individual lots were cut using the ‘Cut Polygons’ tool.  I can display the geometries verticies (the corners or deflections of a line) which allows me to easily snap from one vertex to another in place of typing in bearings and distances. Once all the lots were cut the subdivision was ready to be placed into the correct geographic position and attributed.

In order to place the subdivision accurately, I use several pieces of information from the plan. For example, the upper left corner is located at the intersection of the centerlines of two roads. Therefore, I anchored the subdivision to that point and then rotated it to the Right of Way (ROW) of the road that is adjacent to the southern boundary of the subdivision. This was a rather easy subdivision to place; however, sometimes using the scale and measuring from objects such as houses, barns, telephone poles, tree lines etc. is required in order for accurate placement.

The final step in adding a subdivision into ArcMap is to add its attributes. Such attributes include: subdivision name, lot number, lot acreage, sequential number of the subdivision, created on and created by. Once finished, you simply save and move on to the next phase which we will look into next month.

I hope this tutorial has given you a better understanding of what a Columbia County GIS Technician does. If you have any questions, please email me or leave it in the comment section below.

Map courtesy of the Columbia County Planning Commission.  Survey by Orangeville Surveying Consultants, Inc.