# N05_E18 Great Lakes pilot: 1996–2026 plat-book page verification and NLDI hydrologic crosswalk **Research date:** 2026-08-11 UTC **Sector:** `N05_E18` — canonical 24 × 24 grid cell, 37.5–45.0° N and 270–285° E (90–75° W) **Anchor:** Merrillville, Indiana, approximately 41.4828° N, 87.3327° W **Time band:** `1950-present`, with 1996 and 2019 local map anchors and a 2026 machine-readable hydrologic crosswalk **Status:** bounded page/image and modern-network verification; no derived score and no `provisional_quadrant` ## Selection and research boundary The preceding 2026-08-10 Lake County plat-book note identified the next defensible step: inspect the relevant scan pages, then compare the publication’s watershed context with an authoritative machine-readable hydrologic source. This run continued the N05_E18 Great Lakes pilot without expanding to another sector or repeating the treaty work. The run retrieved the Internet Archive PDF derivatives for the 1996 and 2019 Lake County plat books, rendered selected pages, checked the page-scoped OCR against the rendered scans, and retrieved the USGS Network Linked Data Index (NLDI) geometry and downstream linked-site response for COMID `3399712`. The output remains a source crosswalk. It does not treat a publication map as a GIS layer, a local catchment as the whole fixed cell, or linked stations as measurements of the entire sector. ## Raw observations ### A. 2019 Lake County plat-book scan - **Archive item:** *Plat Book Lake County, Indiana (2019)*, item identifier `plat-book-lake-county-indiana-2019-images`. - **Catalog/derivative facts:** the item exposes a PDF, OCR text, OCR XML, page-number JSON, scan data, and JP2 image archive. The retrieved PDF is 86 pages. The item metadata names the Lake County Soil & Water Conservation District and Mapping Solutions GIS in the publication description. - **Rendered page 4 / printed page 2:** the scan shows the `KEY MAP OF LAKE COUNTY, INDIANA` map section. The page-scoped OCR identifies `LAKE MICHIGAN`, county/township map context, page boundaries, and township/range legend text. Some map lettering is difficult for OCR; the image, not the OCR string, is the controlling object for ambiguous labels. - **Rendered pages 30–31 / printed pages 28–29:** the scans show the two-page `Hobart Townships 35N & 36N - Ranges 7W & 8W` map section. The page-scoped OCR preserves the section title and the continuation/page-reference text. This is the local map plate nearest the Merrillville/Gary/Hobart anchor in the 2019 book. - **Rendered page 53 / printed page 51:** the scan shows the `WATERSHEDS MAP`. The page-scoped OCR identifies `LAKE MICHIGAN`, `Thorn Creek`, `Crooked Creek-Kankakee River`, `Knight Ditch`, and `Kankakee River` labels, and the printed explanatory text stating that identified watersheds are classified by the USGS as HUC-10 and are typically 62–390 square miles. The 62–390 square-mile range is retained as the book’s printed explanation, not independently recomputed here. - **Source lineage stated in the book:** the 2019 OCR and rendered pages identify 2018 USDA NAIP imagery and USGS NED-derived elevation as inputs described by the publication. The underlying rasters were not retrieved in this run. ### B. 1996 Lake County plat-book scan - **Archive item:** *Plat Book Lake County, Indiana (1996)*, item identifier `plat-book-lake-county-indiana-1996-images`. - **Catalog/derivative facts:** the item exposes a PDF, OCR text, OCR XML, page-number JSON, scan data, and JP2 image archive. The retrieved PDF is 61 pages. The item identifies the Lake County Soil & Water Conservation District and Athentic Inc. in the publication description. - **Rendered page 35:** the scan shows the `HOBART TOWNSHIP 35-36 N. RANGE 7-8 W.` map heading and township/range context. This verifies that the 1996 book contains a local Hobart map plate, but the scan does not by itself provide georeferenced boundaries for `N05_E18`. - **Rendered pages 46–49:** the scans show the 1996 `INDEX OF OWNERS • LAKE COUNTY` pages. The OCR includes entries such as `Gary City School`, `Gary Water`, `Gary Steel Products Corp.`, and `Elgin-Joliet & Eastern RR` in township/section-index context. These are publication index entries, not operating records, ownership adjudications, production values, or infrastructure measurements. - **Publication limitation:** the 1996 city-street-map notice states that map information came from various state, county, and city sources and was not field checked by the publisher. That warning is material source-bias and measurement-quality metadata. ### C. USGS NLDI machine-readable crosswalk - **Starting feature:** USGS NLDI COMID `3399712`, retrieved as a GeoJSON feature collection from the official API. - **Reach response:** the COMID endpoint returned one NHDPlus COMID feature with a LineString geometry. The retrieved LineString has 27 coordinate vertices. Its properties identify `source=comid`, `sourceName=NHDPlus comid`, and `comid=3399712`. - **Local basin response:** the `/basin` endpoint returned one GeoJSON polygon. The returned polygon has 27 coordinate vertices and a bounding box of approximately 87.365025–87.316221° W and 41.449326–41.486446° N. All returned vertices fall within the canonical N05_E18 latitude and longitude bounds. This is a local NHDPlus/NLDI basin footprint, not the full 15° × 7.5° sector. - **Downstream linked sites:** `/navigation/DM/nwissite` returned 19 downstream NWIS surface-water sites. The first returned feature is `USGS-413548087131901`, `COUNTY LINE RD DITCH AT STAGECOACH RD NEAR IDNL`, with COMID `3398192`, reachcode `04040001000022`, and navigation measure `96.4958`. The response is a network-linked site discovery result, not a claim that all 19 sites have observations for the same date, analyte, method, or period. - **Date and units:** API retrieval was performed 2026-08-11 UTC. Coordinates are GeoJSON longitude/latitude values in decimal degrees as returned by the API; the NLDI response does not provide a cell-wide area or a population/energy measure. ## Source interpretation 1. The rendered 2019 pages verify that the previously located OCR references correspond to actual key-map, Hobart township/range, and watershed-map scan pages. This improves page-level provenance while leaving map digitization and georeferencing undone. 2. The rendered 1996 pages verify a local Hobart map plate and the index-page context for named Gary/Merrillville-area properties and transport references. The index entries are leads for primary administrative records, not evidence of facility operation or capacity. 3. The 2019 watershed map and the USGS NLDI response are related but not equivalent. The book presents a county-level printed watershed classification; NLDI supplies a machine-readable local network/catchment object tied to a COMID. Neither source alone defines the fixed 24 × 24 cell’s hydrologic composition. 4. The NLDI basin’s returned footprint lies inside the fixed cell’s bounding box, which supports a bounded local hydrologic anchor around Merrillville. It does not establish that the entire N05_E18 cell drains through that basin, nor that the basin is representative of the Great Lakes industrial corridor. 5. The book’s source-input statements for 2018 NAIP and USGS NED provide a reproducible lineage lead. They do not authorize back-calculating land cover, elevation, watershed share, or infrastructure from the publication’s printed maps. ## Geography and variable crosswalk | Source observation | Modern/canonical target | Relation | Limitation | |---|---|---|---| | 2019 key map and Hobart township/range plates | Fixed `N05_E18` geometry | related, not equivalent | Printed pages were verified but not georeferenced or clipped to the cell | | 2019 watershed map and printed HUC-10 explanation | USGS HUC/NHDPlus/NLDI features | related, not equivalent | County map classification and modern network objects have different footprints and production methods | | USGS NLDI COMID `3399712` local basin | Hydrologic subunit inside the fixed cell | potentially directly comparable as a local geometry | The basin is a local catchment, not a cell-wide or corridor-wide measure | | USGS NLDI downstream NWIS site list | Water-monitoring network connectivity | related, not equivalent | Linked-site discovery does not establish sampling dates, analytes, units, qualifiers, or data completeness | | 1996 owner index entries | Industrial/transport historical records | named-feature lead | Index text does not establish ownership validity, operating status, capacity, emissions, or dates | | 2019 NAIP/NED statements | Contemporary raster/elevation datasets | source-lineage lead | Underlying source layers were not retrieved or measured here | ## Derived layer No constraint score, adaptive-capacity indicator, population value, energy value, watershed-share percentage, route length, or formula output was calculated. The only bounded geometric statement is a source-footprint check: every coordinate returned in the NLDI local-basin polygon falls within the canonical N05_E18 latitude/longitude bounds. This is a spatial containment diagnostic, not a score and not evidence that the basin represents the whole sector. ## Model classification - `provisional_quadrant`: `unresolved` - **Reason:** the plat-book pages are publication maps and indexes rather than cell-wide machine-readable measurements; the NLDI object is a local catchment and linked-network response; the nine-sector pilot still lacks comparable raw-observation tables and a frozen formula. - **Model boundary:** `provisional_quadrant` is a model output and is not an archival fact. ## Missingness and uncertainty - `map_georeferencing_missing`: rendered pages were verified, but no georeferenced raster, control points, or digitized map layer was created. - `fixed_cell_hydrologic_composition_unresolved`: one local NLDI basin cannot characterize the full canonical cell. - `source_layer_unretrieved`: the 2018 NAIP and USGS NED layers named by the 2019 book were not retrieved from their custodians. - `historical_continuity_unresolved`: 1996 and 2019 plat books are dated publication anchors, not a continuous land-use or ownership time series. - `facility_status_unresolved`: 1996 index entries are not operating, permitting, emissions, or production records. - `network_observation_missing`: the NLDI downstream response identifies linked NWIS sites but does not supply a harmonized observation table for dates, analytes, methods, units, qualifiers, or detection limits. - `watershed_crosswalk_partial`: the book’s watershed map was not digitized and no HUC-10 polygon intersection with the fixed cell was computed. - `not_applicable`: no score or quadrant formula was attempted. No archival silence, OCR omission, inaccessible derivative, missing station observation, or non-overlap was converted into zero. ## Next search path 1. Retrieve and inspect the remaining 2019 key-map, Hobart township, county-road, and watershed scan pages at page/image level; preserve the Archive.org leaf/page identifiers and distinguish printed page numbers from PDF page numbers. 2. Retrieve the corresponding 1996 map and index pages needed to separate map labels, advertisements, and directory entries; use them only as leads until primary records are found. 3. Obtain authoritative HUC-10/WBD or NHDPlus polygon objects and calculate an explicit, reproducible intersection with the fixed `N05_E18` geometry; report boundary uncertainty and do not infer a cell-wide value from COMID `3399712`. 4. Continue the separate primary administrative-record search for Gary Works, Gary Water Works, railroads, pipelines, permits, and remediation; do not substitute plat-book index text for those records. 5. Complete comparable raw-observation tables for the nine Great Lakes sectors before assigning any quadrant. ## Provenance register | Evidence | Tier | Identifier / page or item scope | Date accessed | URL | |---|---|---|---|---| | 2019 Lake County plat-book scan | C: digitized local map/publication source | Item `plat-book-lake-county-indiana-2019-images`; PDF pages 4, 30–31, and 53; printed pages 2, 28–29, and 51; rendered scan/OCR cross-check | 2026-08-11 | | | 2019 PDF derivative | C: digitized scan | `Plat BookLakeCountyIndiana2019_images.pdf`; 86-page scanned publication | 2026-08-11 | | | 2019 OCR derivative | C: locator/transcription aid | `Plat BookLakeCountyIndiana2019_images_djvu.txt`; page-scoped passages for key map, Hobart plates, and watershed map | 2026-08-11 | | | 1996 Lake County plat-book scan | C: digitized local map/publication source | Item `plat-book-lake-county-indiana-1996-images`; PDF pages 35 and 46–49; rendered scan/OCR cross-check | 2026-08-11 | | | 1996 PDF derivative | C: digitized scan | `PlatBookLakeCountyIndiana1996_images.pdf`; 61-page scanned publication | 2026-08-11 | | | USGS NLDI reach | A: authoritative machine-readable API | COMID `3399712`; one LineString feature, 27 coordinate vertices | 2026-08-11 | | | USGS NLDI local basin | A: authoritative machine-readable API | COMID `3399712` `/basin`; one polygon, 27 coordinate vertices; returned coordinate bounds recorded above | 2026-08-11 | | | USGS NLDI downstream NWIS links | A: authoritative machine-readable API | COMID `3399712` downstream navigation to `nwissite`; 19 linked features | 2026-08-11 | | | USGS NLDI method documentation | A: institutional technical documentation | NLDI indexes flowpaths/catchments and provides basin/navigation services | 2026-08-11 | | | Canonical sector definition | A: project record | `N05_E18`, 37.5–45.0° N, 270–285° E; Merrillville anchor | 2026-08-11 | `N05_E18_MERRILLVILLE-sector-record.json` | ## Bottom line This run verifies the relevant 1996 and 2019 Lake County plat-book scan pages and adds a machine-readable USGS NLDI local-basin and linked-site crosswalk around the Merrillville anchor. The evidence chain is stronger at the page/item and modern-network levels, but the fixed-cell hydrologic composition, georeferenced historical map layers, primary facility records, comparable nine-sector tables, and model classification remain unresolved. The next defensible step is an explicit HUC-10/NHDPlus/WBD-to-`N05_E18` intersection with preserved boundary uncertainty, followed by primary administrative-record retrieval—not a score.