feat(docs-welcome): add quick concepts section

Author: uw-amy-bordenave

docs/index.md

@@ -32,6 +32,53 @@ _Additional TCAT projects can be found [on the TCAT website](https://tcat.cs.was
 
 ---
 
+### Quick Concepts
+
+??? question "What is OS-CONNECT?"
+
+    **OS-CONNECT** (OpenSidewalks COnsistent Network for accessible Navigation and Equitable Connectivity through Transit) is a comprehensive, high-resolution, connected pedestrian network dataset for Washington State. Created under the directive of the Washington State Legislature, OS-CONNECT provides detailed sidewalk infrastructure data across 320+ cities and counties, supporting Washington's goals around transportation equity, safety, and accessibility.
+
+    [:octicons-arrow-right-24: Learn more](os-connect/index.md)
+
+??? question "What is the TDEI?"
+
+    The **Transportation Data Exchange Initiative** (TDEI) is a shared, standardized framework for transportation data that enables seamless integration across mobility systems. The TDEI provides infrastructure for collecting, storing, maintaining, and sharing open data about sidewalks, transit paths, and on-demand transit services, laying the groundwork for more effective transportation planning and innovation.
+
+    [:octicons-arrow-right-24: Learn more](tdei/index.md)
+
+??? question "What is OSW / OSW Schema?"
+
+    **OpenSidewalks** (OSW) is an initiative led by TCAT to provide a comprehensive, accessibility-forward specification for mapping sidewalks and related pedestrian infrastructure. The **OpenSidewalks Schema** is the open data standard that promotes an explicit network (graph) model. Its primary features are defined as connected Nodes (points) and Edges (lines) representing a traversable, graph-analyzable pedestrian network of sidewalks, street crossings, and other paths, along with data representing potential barriers such as stairs and raised curbs.
+
+    [:octicons-arrow-right-24: Learn more](opensidewalks/index.md)
+
+??? question "What is a Connected Network?"
+
+    A **connected network** is a graph of pedestrian infrastructure such as sidewalks, crossings, curb ramps, and other paths where all elements are linked as Nodes, Edges, and Zones forming a complete, traversable network. This is in contrast to disconnected or partial datasets where features exist in isolation.
+
+    **Why this matters:**
+
+    - **Routing** — A connected network enables turn-by-turn pedestrian navigation and accessibility-focused trip planning (as in [AccessMap](accessmap/index.md)), because every path segment connects to the next.
+    - **Analysis** — Connectivity allows for network-level analyses (such as [walksheds](walksheds/index.md)), enabling gap detection and equity assessments, computations that require understanding how infrastructure elements relate to one another.
+
+??? question "What is a POI?"
+
+    A **Point of Interest** (POI) is a specific, identifiable location that is relevant to pedestrians or travelers, such as a transit stop, park entrance, business, public facility, or other amenity. In the context of TCAT projects, POIs are used alongside pedestrian network data to analyze access to destinations and services.
+
+??? question "What is a Walkshed?"
+
+    A **walkshed** is the area reachable via a specified mode of transport from a given location within a specified travel time or distance, considering the actual pedestrian network. Unlike a simple radius, a walkshed accounts for real-world path connectivity, barriers, and infrastructure conditions. The [TDEI Walksheds](walksheds/index.md) tool uses pedestrian network data to compute and visualize these areas, enabling analysis of access to amenities and services.
+
+    [:octicons-arrow-right-24: Learn more](walksheds/index.md)
+
+??? question "What is a Routing Profile?"
+
+    A **routing profile** is a set of preferences and constraints that customize how a pedestrian route is calculated. For example, a routing profile may specify maximum acceptable incline, preference for curb ramps, or avoidance of unpaved surfaces. Tools like [AccessMap](accessmap/index.md) use routing profiles to generate personalized, accessibility-aware directions based on individual needs.
+
+    [:octicons-arrow-right-24: Learn more](accessmap/index.md)
+
+---
+
 ### Resources
 
 - **[Guides List](guides-list/index.md)** — User manuals, tutorials, and technical documentation