# N05_E18 Great Lakes pilot: 1996–2019 plat-book page verification and USGS NLDI anchor **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 current hydrologic-network observation **Status:** bounded page/image and machine-readable network crosswalk; no derived score and no `provisional_quadrant` ## Selection and research boundary The prior 2026-08-10 plat-book note identified the next defensible search path: retrieve and visually inspect the relevant Lake County 1996/2019 pages, then obtain an authoritative modern hydrologic object before deriving any overlap. This run did not repeat the prior catalog discovery. It downloaded the Archive.org PDF derivatives, rendered selected pages, checked the page-scoped OCR against the scans, and queried the official USGS Network Linked Data Index (NLDI) for the existing local COMID `3399712` anchor. The selected material remains bounded. A plat book is a publication-specific map and landownership source, not a legal cadastral database or a cell-wide infrastructure, population, hydrology, or energy dataset. The NLDI basin is a local catchment associated with one COMID, not the canonical sector’s full drainage or land/water composition. No score, area share, route length, or model classification is derived. ## Raw observations ### A. 2019 Lake County plat book: inspected scan pages **Archive.org item:** *Plat Book Lake County, Indiana (2019)*, identifier `plat-book-lake-county-indiana-2019-images`. The PDF derivative has 86 pages. The item also exposes OCR text/XML, page-number JSON, scan data, and JP2 images. The following observations were checked against the rendered PDF pages. Page references below are PDF leaf/page numbers, with the printed map page shown where legible. 1. **PDF page 4 — key map.** The scan visibly presents `KEY MAP OF LAKE COUNTY, INDIANA`, with `LAKE MICHIGAN` at the north, county and city boundary symbols, page-boundary and township/range indications, and a `NEWTON COUNTY` label at the southern edge. The page is a county-level orientation map. It is not a georeferenced polygon. 2. **PDF page 30 — Hobart map plate.** The scan visibly presents `Hobart Townships 35N & 36N - Ranges 7W & 8W`, with printed map page `28`. This is a source-footprint confirmation for the Merrillville/Hobart corridor, not proof that the entire plate lies inside `N05_E18`. 3. **PDF page 31 — continuation plate.** The scan visibly presents the continuation `Hobart Townships 35N & 36N - Ranges 7W & 8W`, with printed page `29` and cross-page references. It confirms the two-page township/range map sequence; it does not establish parcel, route, or watershed totals. 4. **PDF page 53 — watershed map.** The scan visibly presents `WATERSHEDS MAP`, `LAKE MICHIGAN`, and regional labels including `Thorn Creek`, `Crooked Creek–Kankakee River`, and `Knight Ditch`. Its explanatory text states that identified watersheds are classified by the USGS as HUC-10 and gives the book’s typical size description of 62–390 square miles. This is a printed map and explanatory claim, not an independently calculated HUC polygon or area measurement. ### B. 1996 Lake County plat book: inspected scan pages **Archive.org item:** *Plat Book Lake County, Indiana (1996)*, identifier `plat-book-lake-county-indiana-1996-images`. The PDF derivative has 61 pages. The item exposes OCR text/XML, page-number JSON, scan data, and JP2 images. 1. **PDF page 35 — Hobart map plate.** The scan visibly presents `HOBART TOWNSHIP 35-36 N. RANGE 7-8 W.` and the map compass. It is a dated local map anchor for the same township/range corridor. The scan does not provide a georeferenced polygon for `N05_E18`. 2. **PDF pages 46–49 — owner index.** The scan visibly presents `INDEX OF OWNERS • LAKE COUNTY` with township and section fields. The pages include entries such as `Gary City School`, `Gary Industrial Fndtn Inc`, `Gary Steel Products Corp`, `Elgin-Joliet & Estrn RR`, `Cities Service Oil Co`, and other named owners or organizations. These are printed index entries. They do not prove current ownership, operation, production, emissions, infrastructure capacity, or cell-wide prevalence. 3. The 1996 book’s map and index are not treated as a continuous time series with the 2019 book. Publication purpose, map construction, feature coverage, and source boundaries differ. ### C. Official USGS NLDI response for the local anchor The existing project record uses COMID `3399712` near Merrillville. On 2026-08-11 UTC, the official NLDI API returned: 1. **Reach object:** `https://api.water.usgs.gov/nldi/linked-data/comid/3399712` returned a GeoJSON `FeatureCollection` with one `LineString` feature and properties identifying the COMID and NHD-derived network object. The returned reach geometry includes coordinates around longitude −87.33 and latitude 41.48. The exact returned object should be treated as the retrieval record; no length was calculated. 2. **Local basin object:** `https://api.water.usgs.gov/nldi/linked-data/comid/3399712/basin` returned a GeoJSON `FeatureCollection` with one polygon feature. The visible coordinate extent is local to the Merrillville anchor, including longitudes approximately −87.365 to −87.316 and latitudes approximately 41.449 to 41.486. This is the local basin associated with the COMID response, not a full-sector basin mask. 3. **Downstream linked-site search:** `https://api.water.usgs.gov/nldi/linked-data/comid/3399712/navigation/DM/nwissite` returned a GeoJSON `FeatureCollection` of downstream NWIS surface-water sites. The first returned feature was `USGS-413548087131901`, `COUNTY LINE RD DITCH AT STAGECOACH RD NEAR IDNL`, at approximately −87.2219444, 41.59666667, with NLDI COMID `3398192` and reachcode `04040001000022`. This is a network-discovery result, not evidence that the site lies inside the fixed cell or that it shares the same historical water system. No NLDI polygon was used as a substitute for the fixed `N05_E18` boundary. The local basin was not intersected with the canonical cell in this run because the cell polygon and a reproducible geospatial calculation pipeline were not yet assembled. ## Source interpretation 1. The 1996 and 2019 scans now have page-level visual anchors for the local township/range map sequence and, for 2019, the watershed map. This improves extraction quality over OCR-only location, but the printed maps remain publication-footprint evidence. 2. The 1996 owner index provides historical named-feature leads for rail, steel, industrial, school, and petroleum-related records. The proper interpretation is “the publication lists these names in these township/section index entries,” not “these entities supplied a measured sector-wide condition.” 3. The 2019 watershed page provides a source-stated HUC-10 classification context. Because no HUC polygon was extracted from the page and no area was measured, the observation remains qualitative and source-specific. 4. The official NLDI response supplies a current machine-readable hydrologic reach, a local-basin polygon, and a downstream discovery path. This is a useful modern anchor for the contemporary end of the bridge, but it has a much smaller and different spatial footprint than the fixed 24 × 24 sector. 5. The archival and modern footprints are therefore related but not equivalent. They should be joined only through an explicit geography crosswalk, not by proximity or narrative continuity. ## Geography and variable crosswalk | Source observation | Modern/canonical target | Relation | Limitation | |---|---|---|---| | 2019 PDF pages 4, 30–31 | Fixed `N05_E18` geometry | related, not equivalent | County orientation and township/range plates were not georeferenced or clipped | | 2019 PDF page 53 watershed map | USGS HUC-10/WBD/NHDPlus objects | related, not equivalent | Printed labels and book explanation do not provide machine-readable boundaries | | 1996 PDF page 35 Hobart map | Fixed `N05_E18` geometry | related, not equivalent | Local map plate has no cell polygon or overlap computation | | 1996 PDF pages 46–49 owner index | Historical infrastructure/industry lead table | qualitative lead only | Index entries do not establish operating status, capacity, or extent | | NLDI COMID `3399712` reach | Current hydrologic network | directly machine-readable for the returned object | One reach is not the full sector hydrology; no length or cell overlap calculated | | NLDI COMID `3399712` local basin | Current catchment crosswalk | related, not equivalent | Local basin is not the fixed cell and was not intersected with it | | NLDI downstream NWIS response | Current network discovery | related, not equivalent | Discovery response does not establish historical continuity or fixed-cell membership | ## Derived layer No numerical sector score was derived. No parcel count, map-feature count, watershed share, basin area, reach length, facility capacity, energy value, population value, constraint score, adaptive-capacity indicator, formula output, or quadrant was calculated. The bounded evidence-chain update is: ```text 1996 page-verified Hobart map + owner-index leads + 2019 page-verified key/township/watershed maps + official NLDI reach/local-basin/downstream-site responses -> improved source and extraction provenance for N05_E18 while fixed-cell geometry, HUC/WBD intersection, and comparable measures remain unresolved ``` ## Model classification - `provisional_quadrant`: `unresolved` - **Reason:** all observations have source-footprint or local-network limitations; no comparable cell-wide raw table or formula application exists. - **Model boundary:** `provisional_quadrant` is a model output and is not an archival fact. ## Missingness and uncertainty - `fixed_cell_geometry_unresolved`: the canonical cell polygon was not constructed in the run. - `huc_or_wbd_geometry_unretrieved`: the printed 2019 HUC-10 context was not converted into authoritative machine-readable watershed polygons. - `map_georeferencing_unresolved`: page scans were visually inspected but not georeferenced. - `local_basin_not_cellwide`: the NLDI basin is one local COMID catchment, not a sector-wide hydrologic measure. - `nldi_reach_length_not_calculated`: the returned geometry was preserved as an object-level observation; no length was derived. - `historical_continuity_unresolved`: 1996 and 2019 are dated map anchors, not a continuous land-use or infrastructure record. - `facility_status_unresolved`: owner-index names do not establish operation, capacity, emissions, or persistence. - `ocr_and_scan_scope_limited`: only selected pages were rendered and checked; the complete plate sets remain unreviewed. - `not_applicable`: no score or quadrant formula was attempted. No archival silence, OCR omission, inaccessible derivative, absent page label, or missing network link has been converted into zero. ## Next search path 1. Retrieve authoritative HUC-10/WBD or NHDPlus polygon objects and calculate a reproducible intersection with the fixed `N05_E18` polygon; retain CRS, dataset version, retrieval date, geometry method, and overlap uncertainty. 2. Render and inspect the remaining 2019 township, county-road, and watershed plates and the relevant 1996 map/index pages; preserve page/image identifiers and distinguish map labels from advertisements and index text. 3. Retrieve the underlying 2018 NAIP and USGS NED products named by the 2019 book only if coverage and a cell-level extraction method can be documented. 4. Continue the separate primary administrative-record search for Gary Works, Gary Water Works, rail corridors, petroleum facilities, permits, and remediation; do not treat plat-book names as operational measurements. 5. Complete the Great Lakes nine-sector comparable raw-observation tables before assigning any quadrant. ## Provenance register | Evidence | Tier | Identifier / page or item scope | Date accessed | URL | |---|---|---|---|---| | 2019 Lake County plat-book PDF | C: digitized local map/publication source | Item `plat-book-lake-county-indiana-2019-images`; PDF pages 4, 30–31, 53 visually inspected; PDF derivative has 86 pages | 2026-08-11 | | | 2019 Archive.org metadata and derivatives | C: machine-readable catalog/scan metadata | PDF, OCR text/XML, page-number JSON, scan data, JP2 derivatives | 2026-08-11 | | | 2019 OCR derivative | C: locator/transcription aid | `Plat BookLakeCountyIndiana2019_images_djvu.txt` and XML; page-scoped OCR cross-checked against selected scans | 2026-08-11 | | | 1996 Lake County plat-book PDF | C: digitized local map/publication source | Item `plat-book-lake-county-indiana-1996-images`; PDF pages 35, 46–49 visually inspected; PDF derivative has 61 pages | 2026-08-11 | | | 1996 Archive.org metadata and derivatives | C: machine-readable catalog/scan metadata | PDF, OCR text/XML, page-number JSON, scan data, JP2 derivatives | 2026-08-11 | | | USGS NLDI reach | A: authoritative machine-readable API | COMID `3399712`; returned GeoJSON reach object | 2026-08-11 | | | USGS NLDI local basin | A: authoritative machine-readable API | COMID `3399712`; returned GeoJSON basin object | 2026-08-11 | | | USGS NLDI downstream linked sites | A: authoritative machine-readable API | COMID `3399712`; navigation mode `DM`; data source `nwissite`; first returned feature `USGS-413548087131901` | 2026-08-11 | | | Canonical sector definition | A: project record | `N05_E18`, 37.5–45.0° N, 270–285° E; no new values derived | 2026-08-11 | `N05_E18_MERRILLVILLE-sector-record.json` | | Research procedure | A: project SOP | Fixed 24 × 24 grid, source hierarchy, page-level provenance, missingness, and model-output boundary | 2026-08-11 | `08-research-sop.md` | ## Bottom line This run completes the next bounded step from the prior plat-book note: selected 1996 and 2019 pages are now visually checked against page-scoped OCR, and the modern hydrologic bridge is anchored to official USGS NLDI GeoJSON responses for COMID `3399712`. The result is better extraction and provenance, not a cell-wide measurement. The next defensible action is to retrieve authoritative HUC-10/WBD or NHDPlus geometry and perform an explicit intersection with the fixed 24 × 24 `N05_E18` polygon; until then, the sector score and `provisional_quadrant` remain unresolved.