Mapping_Methodology.doc

 

 

The purpose of this document is to provide the users of the NJDEP State Owned, Protected Open Space and Recreation Areas (NEWSTATE) shapefile with a detailed description of the numerous mapping methodologies and data limitations associated with the data file. Included are descriptions of the original mapping project, interim mapping methodologies and current mapping procedures.

 

Original Mapping Project:

 

The foundation of this State owned and protected, open space data set originated with the generation of an ArcInfo coverage called Open91. Its data generation began in 1989 and was digitally released in 1991.  Its initial purpose was to provide Natural & Historic Resources in DEP with a manageable, graphic inventory of state owned and protected open space in New Jersey.

 

Original source map information:

 All State-owned, protected, open space boundary lines were taken from hand-drafted  

 delineations as they appeared on in-house 1:24000 USGS  paper topoquads. These hand-drafted  delineations mapped by the Divisions of Parks & Forestry or Fish & Wildlife varied greatly with  regard to degree of accuracy, level of completeness & mapping methodology. In many cases,  updates to these paper topos had been made sporadically over   the years by different individuals with no documentation of the sources used or dates revisions were made.

 

Original mapping methodology:

 The boundary lines from the above mentioned paper source maps were transferred to

 a newly acquired set of DEP standardized base maps,1986 1:24,000 photoquads.

 Mylar sheets were overlayed and registered to each photoquad.  Each boundary line segment   was then manually transferred to the mylar overlay matching the same cultural and physical features evident on the paper map (e.g.,roads, watercourses, ditches). 

 Aerial photos were also examined to refine the placement of numerous boundaries

 poorly depicted or omitted on the source, but evident on the photoquad image; boundaries such as, watercourse meanders, hedge rows and old field lines.  If a boundary line did not follow a visible feature on the source map or photoquad, it was locally fit based on surrounding features

 common to both sources.

 

Original mapping criteria:

 All State protected open space parcels appearing on in-house topos were

 mapped. Where the boundaries of two adjacent open space parcels (mapped by

 different divisions) overlapped, one was arbitrarily  selected over the other to avoid confusion in parcel coding and visual presentation.  It was not important at that time to demarcate interior  ownership boundaries of existing protected open space parcels;

 discrepancies could be resolved in the future if need be.

 

Original mapping accuracy & data limitations:

 These hand-drafted topoquad lines were 2^nd or 3^rd generation depictions; their accuracies were unknown.  Their systematic transfer onto the 24,000 photoquad enabled them to be entered into the GIS without further corruption and possibly with some positional improvement.  These delineations were intended to provide the foundation for a statewide, visual, inventory of existing

 protected, open space to aid in future acquisition strategies. It was never intended to be a substitute for survey quality line placements or deed ownership. Lines were inked with a 000 pen and then manually digitized. Digital proof plots were generated for each quad and compared to the original mylar delineations; all digitization errors greater than a line width(10ft.)were corrected.

 

 

Interim Mapping Methodologies:

 

After 1991, keeping pace with new computer technologies, the mapping methodologies changed significantly. The 1991, 1:12000 quarter-photoquads became the new standard base map. The parcel boundaries of most new acquisitions were obtained from current tax book maps; the in-house topos were no longer used. In addition, all interior lot lines were drafted and digitized. New attributes were added to record block, lot and municipal affiliations.

 

Tax map delineation evolution:

Initially, individual block and lot lines were photocopied from individual tax map sheets then re-scaled to fit 1991, 1:12000 quarterquad base maps. These lines were reoriented to match the image features on the quarterquads. Next, the lines were drafted onto mylars registered to the quarterquads, labeled with block/lot numbers then manually digitized into the GIS.

 

Then in 1993, electronically published tax maps were made available and 1: 12000 digital ortho-photoquads could be accessed in ArcInfo. Tax maps were then converted to tiff files, and rectified to the digital orthophotoquads. Once RECTIFIED, individual lot lines could  be drafted on screen. This new technology replaced the re-scaling, drafting on mylar and manual digitization steps; it greatly improved the efficiency of the mapping process.

 

Data Limitations:

Boundary line accuracy of tax maps are unknown. Their depictions are  less than “reasonably” accurate but they improved when re-drafted onto 1:12000 photo base maps using coincident features. Placement further improved when rectified on screen to 1:12000 1991 and later, 1995 1:12000 orthophotos.

 

 

Current Mapping Methodologies:

 

 Since 1995, the bulk of acquisitions are entered into the GIS using a certified survey of the    property boundaries. The ArcInfo Cogo program facilitates the incorporation of deeds and surveys. Much effort is made to enter data within a year of the purchase. Tax map lines are utilized only if a survey does not exist.

 

Survey lines:

 When surveys are available, a COGO program converts a CAD file of the parcel to an ARCINFO coverage polygon. A Nad83 or Nad27 NJSPC certified survey is the best available source with regard to shape and positional accuracy.  Non-NJSPC certified surveys provide the best parcel shape but not position. They are repositioned to fit the features present on the on-screen image. If interior lot lines are omitted on either type of survey, then tax map lot lines are added  using the “best fit” method mentioned above.

 

Tax map lines:

The appropriate pages from a current tax book are scanned, saved as tiff files and brought into the GIS and rectified using an ARCinfo/ArcMap program and 2002 digital imagery. Only the property lines that compose the acquisition are digitized on screen and added to the coverage.  Attributes are added and coverage is cleaned or built.

 

Current Mapping Accuracies & Data Limitations:

To date, over 6200 parcels have been added to the State open space coverage. The goal is to map all newly acquired open space parcels in a timely fashion with the best information available. It cannot be stressed enough, that due to the dynamic nature of land acquisition business, and time delays associated with the acquisition process itself, this GIS inventory will always be incomplete. Boundary adjustments to the earlier drafted parcels will not occur unless inconsistencies /overlaps arise between those delineations and new acquisitions. At that time, if possible, positional problems will be resolved as well as any tax record inconsistencies. The program does not actively update static areas.  It is too expensive to survey or too time consuming to go through old tax books or deeds to update boundary lines. Where the drafted boundaries of two adjacent parcels misalign (because they were mapped independently of each other or from different sources), the lines from the "better" source are always used.  Surveys will always take precedence over all other map sources.   NJSPC surveys take precedence over all other types of surveys.