What is a Plat Map?
A plat map (also called a subdivision plat or recorded plat) is an official map filed with the county that shows how a piece of land has been divided into individual lots, blocks, and streets. Plat maps record the exact dimensions and boundaries of each lot, the locations of streets and rights of way, easements for utilities and drainage, and any common areas or dedicated public spaces. Every subdivision in the United States is created through the platting process, and the recorded plat is the legal document that defines how the land is divided.
When you buy a property in a subdivision, the legal description in the deed refers to the plat. A typical legal description might read "Lot 14, Block 3, Willowbrook Section 2, a subdivision in Harris County, Texas, according to the plat recorded in Volume 287, Page 42 of the Map Records of Harris County." The plat is what gives legal meaning to "Lot 14, Block 3" -- it defines exactly where that lot begins and ends.
What plat maps show
A complete plat map includes lot dimensions and boundaries for every lot in the subdivision, block numbers and lot numbers, street names, widths, and right of way lines, utility easements (typically along front and rear lot lines), drainage easements and detention areas, common areas and green spaces, building setback lines (in some plats), total acreage of the subdivision, and the surveyor's certification and county recording information.
Plat maps are recorded as public documents and can be viewed at the county clerk's office or, increasingly, through online county GIS systems. Many title companies also maintain plat map archives. When evaluating a property, reviewing the plat provides context that a standard survey of the individual lot may not show -- such as nearby drainage features, planned streets, or easements that affect the property from adjacent lots.
Plats and property research
Investors use plat maps for several research purposes. Comparing actual lot dimensions to tax records identifies discrepancies that may affect value. Identifying easement locations helps evaluate development potential and building constraints. Reviewing drainage patterns and detention areas reveals flood risk that may not be captured in FEMA flood zone maps. And understanding the overall subdivision layout helps assess the neighborhood's character and future development potential.
For lot split analysis, the original plat shows how the lot was created and what restrictions apply. Some plats include minimum lot size requirements or deed restrictions that govern future subdivision. If you're evaluating a large lot for splitting potential, the plat is one of the first documents to review alongside the current zoning code.
Replats and amended plats
When lot lines need to change after the original plat is recorded, a replat or amended plat is required. This process is used for lot splits, lot combinations (merging two lots into one), boundary adjustments between adjacent lots, and changes to easement locations or right of way dedications. The replat process requires a new survey, planning department review, and typically a public hearing before the amended plat can be recorded.
Replats are relevant for investors because they represent changes to the original subdivision layout. A property that was recently replatted from one lot into two may have different characteristics than surrounding properties. Reviewing the replat history helps understand how the property's configuration has evolved and whether any conditions or restrictions were placed on the new lots as part of the replat approval.